my strongest trollers for solo are Dark/Poison (also works very well in PVP, as an aside)
Mind/Storm is highly survivable, but has low DPS so you would probably want to rely on a lot of temp powers to solo properly.
I've had great results with Fire/TA, which I found more suited to solo play than Fire/Rad or Fire/Kin because it offers better control than those, thus keeping the enemies off you.
Similarly Plant/TA is very strong. Come to think of it, Plant is a very underrated set.
Much is going to depend on your personal play style of course so go to town :)
