17-Fret or 19-Fret?
The idea that Irish tenor banjos are supposed to be 17-fret short-scale banjos is probably the biggest misconception when it comes to this style of playing. While it's perfectly fine to use a 17-fret banjo with a 20 to 21 inch scale, the vast majority of top-level and/or professional players use a 19-fret tenor banjo with a scale length between 22 and 23 inches. There may be some advantages to a 17-fret model for some players, but the idea that 17-frets is the standard seems to have originated in America and is related to marketing rather than reality. As I have discovered recently, 19-frets is not that much more of a reach over the first five frets, but the extra scale length creates more tension on the strings, which can make them more responsive and easier to play.
The resonator versus open back question gets asked a lot and the short answer is resonator. Again, if you base it on popularity, most experienced players have always gravitated towards resonator banjos, with a couple recent notable exceptions such as John Carty (an open back 19-fret Ome nowadays) and Angelina Carberry (an open back 17-fret Oakwood). These kinds of things can be subject to trends and the fact that some prominent players are currently using open backs may have a trickle down effect. Resonators punch through more in a session setting, which may not be what you are looking for if you are a less than confident player. An open back may allow you to blend in better (be less of a nuisance!) and they are also lighter, which has ergonomic benefits. The resonator is more quintessential.
Tuning - GDAE or CGDA (or ADAE, et cetera)?
The 5ths tuning of GDAE (from low to high) is the standard for Irish tenor banjo. This tuning, which mimics the tuning of a mandolin or fiddle but is one whole octave lower, suits the keys/modes most commonly encountered in Irish music. Outside of the Irish tradition, tenor banjo is still usually tuned in 5ths but those pitches are CGDA. While beneficial for a lot of music, CGDA is not as versatile in Irish trad where there are benefits to using GDAE instead. Since most sets of tenor banjo strings are designed for CGDA, you kind of have to assemble your own customized sets of heavier strings for GDAE. There are some pre-packaged "Irish" sets, but there remains a lot of debate over what gauges to use and I am not qualified to comment on that here! Another tuning that some Irish tenor banjo players use is ADAE. By tuning the low G up a whole step to A you help solve potential string floppiness issues and also open up additional droning possibilities.
Melody or Chords?
This is an easy one. Unlike the chordal style found in jazz banjo, Irish tenor banjo is quite purely melodic. You won't find many examples of people using a tenor banjo as a long-term chording/rhythm/backup instrument in Irish music. In the right hands, the tenor banjo is a melodic equal to the fiddle, flute, accordion, concertina, pipes or any other instrument used to interpret these classic tunes. An Irish tenor banjo player plays the melody almost 100% of the time in unison with the other melody instruments present. Unlike bluegrass where a guitarist or mandolinist might strum or chop until it's his turn to solo, in Irish music you basically solo all the time as part of the larger group, within the confines of the tune. Some mindful advanced players are more supportive and responsive in the tenor banjo role, but are still playing the head melody in unison with everyone else.
4-strings or 5-strings?
This seems obvious but I was 30 years old the first time I recall seeing an Irish tenor banjo in action or even knowing that such a thing existed. At the time I had never played an instrument before so I had no practical knowledge of music outside of being a listener. I don't think I even noticed that the Irish banjo only had 4-strings, but yes it does. With the 4-strings and GDAE tuning a better name for the tenor banjo might be octave banjolin. The main thing that makes it a banjo is the skin-like material stretched over a rim. The 5-string banjo as found in bluegrass, old-time, folk is something totally different. Irish tenor banjo playing has more in common with mandolin than it does with 5-string banjo.
Plectrum or Fingerpicking or Clawhammer?
For Irish tenor banjo people use a pick (AKA a plectrum). This is like the pick one would use to play guitar. In fact, it usually is a guitar pick. The cheap, grey nylon .73mm (or .60mm) Dunlop or Fender picks seem to be the ones most preferred by Irish tenor banjo players. After a lot of experimenting I now use these types of picks as well. For this reason, playing Irish tenor banjo is sort of like flat-picking guitar. I have read that some people use a thimble instead of a pick, but I've yet to see it done in person. Using your fingers - like on guitar fingerpicking or clawhammer banjo - or actually using finger picks - like the 5-string player Bela Fleck does - is generally not done in Irish music. This doesn't mean that it can't be done, but it would be going against the grain to do so.
First Position or Up the Neck?
Irish tenor banjo players like to stay in first position between frets 2 and 5 except when having to reach up to that pesky high-B on 7th fret of the E-string or sliding up to the occasional 7th fret on one of the other strings. The area beyond the 7th fret tends to be unexplored territory. This is mostly due to the nature of the music (Irish mandolin players also stay in first position) but is partially due to the nature of the instrument. On a guitar (because of how it is tuned) and on a mandolin (because of its shorter scale length) it is feasible to play almost any melody anywhere on the neck in a closed position without having to use open strings, but on a tenor banjo this is not as doable. Some advanced Irish players are able to go up the neck in moderation, but it is not necessary and the technique can be quite complex for casual players.
11" or 12" Rim?
An 11" rim (with a resonator and an arch top tone ring) is the most common, i.e. traditional, but this could be just as much due to the lack of options as it is to a stylistic preference. A few more players seem to be experimenting with 12" rims and liking the sound, and again this is something that can be subject to fads. With more custom builders entering the tenor banjo market, the possibility for greater experimentation is there. A larger rim will likely place the bridge more toward the middle of the skin which could be off-putting if you are used to it being closer to the tailpiece.
New or Vintage?
Here's where it starts to get murky. A lot of people swear that vintage is the only way to go and that you need to have a Paramount, or a Silver Bell, or a Clifford Essex, or an Epiphone, or a Gibson, et cetera. There are lots of different opinions and personal preferences. I happen to like modern, newer banjos and being left-handed I can get side position dots on the left-handed side of the neck if custom ordered. Some of the modern builders include Clareen, Emerald, Ome, Nechville and Deering, as well as smaller boutique builders like Romero, Franzke, Tommy George and JP Banjos. It is often more cost effective to buy a vintage banjo over a modern one, except in cases where the price of the vintage model has been jacked up due to supply vs. demand. Vintage banjos also have greater re-sale value. However, with a modern banjo from a trusted builder you know you are getting something with a perfectly set up neck, a truss rod, upgraded tuners, and so on. The price is also sometimes flexible with a modern builder if you can eliminate aesthetics like inlay without sacrificing other factors like build quality, sound quality and playability.
Triplets, Triplets, Triplets
Ornamentation is at the foundation of Irish music and the Irish tenor banjo player's number one ornament is the triplet. Due to the tenor banjo's lack of sustain notes decay quickly. I suppose the triplet is used to spice tunes up and cover for this. The trick is to learn to pluck the triplets smoothly and use them tastefully, which is something that all Irish tenor banjo players grapple with. It is more important to play the tune well than it is to add in a bunch of triplets. I like the sound of players who use the triplet sparingly, and who also incorporate things like small-chord-double-stops, slides and even string bends to vary the melody.
Irish Tenor Banjo Players
There are several great players and I'm sure I will leave some out, but a short list includes John Carty, Angelina Carberry, Kevin Griffin, Mick Moloney, Barney McKenna, Eamon O'Leary, Enda Scahill, Kieran Hanrahan, Daithí Kearney, Claudine Langille, Dan T. Neely, Brian McGrath, Darren Maloney, Eamonn Coyne, Mick O'Connor, Gerry O'Connor, Stevie Dunne, Brian Connolly and Pauline Conneely.
No banjos were harmed during the writing of this message.