I play Liszt 2 and Tchaik 1.
Liszt 2 isn't that bad, but it has it's nasty moments, and musicaally it is very hard and very weird.
Tchaik one is very awkward, and doesn't fit well under the hand AT ALL. It's awkward to phrase and get good fingerings that actually work. 2nd mvt Presstissimo is the hardest section.
I think Liszt one is hard. I havn't played it properly, but i have spent time on it. It's very pianistic, full of leaps and fast passages. But it fits nicely under the hand.
Rach 1 is very hard. It has some really nasty moments. Again I havn't played this, and don't think I ever will becasue I just don't like it enough, and it would take a lot of hard work.
What other concerto's have you played?