Anyway I feel like answering. Sorry to judge you, but I have to answer your question based on the # of posts you have-- there are very few classes that can solo after level 52 or so without buffs and without significant periods of downtime. Dagger classes and gladiators can solo effectively without being slowed down with mana or health issues, but only if they have buffs or spam health pots.
I think you may be basing the idea of soloing on that everyone before level 20 and often before level 30 don't group. After level 30, it becomes very easy to group, and at the same time, grouping becomes a more effective way of grinding.
Although this whole post is making a huge assumption ^.^
Regardless I'll answer your question-- I personally suggest TH. A large part of a TH's strength lies in his/her passive abilities. THs have good attack speed, running speed, crit rate and health, making them effective at soloing. In C3 they were notoriously gimped but in C4 they seem to have been tweaked and are slightly better (correct me if I'm wrong).
Treasure Hunters get lots of cool skills that messes with the mobs' heads. I especially like "trick" (makes mob not attack you) it's good for when you have pulled one too many mobs. Then there's silent step, veil(sp?) and fake death. All awesome skills.
Gladiators strike me as boring, and if you want to play a male character, do not go glad. It will make your eyes bleed, once you hit B grade and up. ;) A plus for gladiators; duals are cool. (Except if you want an SA on your weapon, and don't have money to buy new duals, if they break).
GO TH more fun skills to play with, and more funthings to grief bots with. If you want dual weps go with a BD not a glad. Glads aren't much anymore but BDs are wanted by everyone now and if you get 76 and beyond BD's have perhaps the most usefull of 3rd class change skills. Dance or petrification.m crit dance, silent step dance =very nice.
TH is the better solo class because they can 1v1 using lure, silent step fake death, what ever, they are superior to a glad in unbuffed PvE, however when buffed a glad is far more devastating and kills faster and takes limited to no damage.
The only thing us glads haveing going for us is our decent pvp abilities.
So for solo play PvE, you want a TH.