Why must I be so indecisive...

I think Sporting Pitchfork’s advice is as sound as it gets. I moved over from GHB–which I played since I was a young teen–after a five year hiatus and it’s been…ahem…an adjustment to say the least. I don’t see why you wouldn’t be able to play a set of SSPs in sessions, especially here in America. But if you don’t already play the GHB (and it seems like you don’t) you’ll have a much easier time finding a teacher…there are something like a million and a half people who play GHB in NYC (ok maybe not that many) but only a handful who play Uilleann pipes. When I learned GHB I spent a year on the chanter before I even touched a set of pipes. Plus, think about it this way…Uillean practice set $500-1500. Practice chanter for GHB $20…second octave however, priceless

mq

Sporting Pitchfork and Crack piper have great advice. You’d be playing different music on smallpipes than uilleann pipes and you will find that uilleanns are more versatile in sessions in America, which are predominantly Irish, than small pipes. As Sporting Pitchfork said, there are Irish tunes that fit on Scottish pipes or have settings designed for Scottish pipes (check out of Daimh playing The Four Courts - I think they changed the key to A or something), but if session playing is your thing, you will have an easier time on uilleanns once you get competent at them. If you want to learn Scottish music or learn highland piping tunes, then smallpipes are the way to go. You can play highland piping tunes on uilleann pipes (not necessarily vice versa), but some of have tricky fingering as they are in A.

In Scotland you are more likely to run into smallpipers and border pipers at sessions than uilleann pipers. In the States it’s the opposite.

It’s true about Scottish pipes at sessions here in the US. The sessions here are Irish sessions usually. I do sometimes bring my SSPs to Irish sessions and whenever I break them out there’s a fiddler or two who take a smoking break! On the other hand there’s a fiddler or two who know a few Scottish tunes and they like the SSPs.
In Glasgow it was very different. I went to a session at Waxy O Connor’s and the music was predominately Scottish. There was a very good “border” pipe player and several fiddlers blasting away at dozens of Scottish tunes I’d never heard (me with 30 years of Highland piping under my belt).
But as people are saying, let the music itself decide. Highland pipes (whether small or full sized) are best for their distinctive music, music which cannot be played very satisfactorily on any other instrument except perhaps for the fiddle. But unless you want to play that repertoire, it’s best to go with the Uilleann pipes.
Obviously the SSPs create an exception, but putting them aside for a moment, what’s interesting is that the milieu or “scene” of Highland pipes and uilleann pipes is perhaps more different than the instruments themselves, or the musics.
Highland piping is about taking lessons from a respected teacher and learning the “right” way to play, about going to solo competitions and being judged, about joining a pipe band and travelling to competitions and all that- a fantastic subculture I’ve spent most of my life in.
Uilleann piping is about going to sessions in pubs, developing a personal style, learning large numbers of tunes so that you can play along as often as possible.
Music is learned completely differently- in the Highland piping scene you learn from sheet music, and practice a very limited repertoire over and over until it is polished to perfection. In the Irish session scene it’s all about how many tunes you play. I see people who are avid session goers who know all the tunes but that, if you really listen to them play alone, really don’t have all that great a mastery of their instrument or its style. In Irish music people usually learn tunes by ear, recording the session they attend and learning the session’s repertoire.
Both of the instruments, and musics, and milieus are equally attractive to me, which is why I’ve spent my life with one foot in each.

"In the Irish session scene it’s all about how many tunes you play. I see people who are avid session goers who know all the tunes but that, if you really listen to them play alone, really don’t have all that great a mastery of their instrument or its style. In Irish music people usually learn tunes by ear, recording the session they attend and learning the session’s repertoire. "

I don’t know which Irish sessions you’re going to. While the sort of things you’re talking about certainly can occur – people learning a zillion tunes without mastering their instrument or style – that is not how I would ever go about characterizing or generalizing about Irish music. It is important to learn lots of tunes, but playing them WELL is regarded as important. In sessions in Edinburgh and Glasgow, it is very hard to get on well unless you’re a good player.

In any case, uilleann piping tradition emphasizes the importance of solo playing, not session playing. Many pipers would advise you not to play pipes in a session, saying that session playing hurts your piping and will damage your ability to develop a personal style. It is not supposed to be an ensemble instrument, but rather a solo instrument, especially if you want to play with drones and regs. Oftimes drones and regs don’t fit in well with a session, as you can’t hear them in a loud pub or they clash with guitar or bouzouki chords. I do play in sessions (usually just chanter – I’ll leave the drones off for the above reasons), but simply because it’s a fun and social thing to do. It may or may not have deleterious effects on my playing, but in any case it is not the ultimate goal of playing uilleann pipes. I think there are very few pipers who would say it is.