I would either go with the HR11 which, as "we" were discussing in another topic, is quite a tricky piece, but certainly not overwhelmingly difficult and, in my opinion, is easily one of the most representative of Hungarian gypsy music out of all the rhapsodies, given its superb cimbalom impersonation in the opening and the folk harmonies near, and during, the friska. It's remarkable, and gets overlooked by the big 10th and 12th rhapsodies on its flanks! Poor little bugger...
...or, I would go with Ende vom Lied, the beautiful, though not without humour surely, closing piece in Phantasiestuck. The whole set is, of course, wonderful (one of my favourite compositions right now, actually), but other neat individual pieces are Fable, Traumeswirren (which actually would be too short to "stand alone" except perhaps as an encore), and In der Nacht. Warum? is also quite popular.
It'd be worth it to learn all of Phantasiestuck, of course, but I understand that's a huge commitment, especially with the Beethoven variations! What a frighteningly enormous piece, well at least for me heh..
Ende vom Lied is substantial, though, and would give you at least 6 minutes of Schumann goodness! If you have the time, perhaps you could play Fable, Traumeswirren, and Ende vom Lied, the three final pieces of Phantasiestuck, and toss in the Liszt Rhapsody for a full circle.
Topic: repertoire suggestions