I really think people worry too much about what to play and not enough about how to play. Really, every class has its weaknesses and strengths, so ultimately any 'best class' arguments are going to come down to the weaknesses you can live with and the ones you can't. To some, sacrificing HP and Def for more offensive abilities is an ideal trade off. Others would much rather have some armor plating instead of a big gun. It all comes down to what you'd rather be able to do, and what you don't mind putting up with.
I have no doubts that Zerkers are a fantastic class at lvl 50+, but how are they at soloing before then? You can't simply start the game with a level 50 Zerker, so it follows to reason that you are going to have to level up to that point. Now when asking whether a class is a good soloing class, it's important to factor in how good they are at the weaker levels as well as the stronger. No, you shouldn't base your opinion of the entire class off of one level range, but you shouldn't ignore those levels either: something that many people do. It's not like Pre 50 Zerkers don't exist. You don't jump from lvl 30 to lvl 50 upon changing.
With this in mind, I have to say that the Paladin class is an exceptional soloing class right from the start. I was able to (and actually did) solo all but a few boss mobs right after promoting at lvl 31. Also remember that when soloing, you've only got yourself to rely on out there. No healer is going to drop out of nowhere to save you, and we all know you can't spam pots. High def, plus healing, plus pulling ability makes the Paladin a very versatile and self reliant class right away, so that's my choice. Doesn't mean any other classes are bad or can't solo, but this class can solo without any trouble right away and never has to worry about any good Samaritans or friends/guildies being around to bail you out. They also aren't under any pressure to keep enemies at a distance or to kill them quickly: when all else fails, you can simply outlast your opponents (which is pretty much what you have to do with bosses).
Last point (and I'm sorry for this long post), this is an MMO. Really, soloing isn't the logic behind any of the classes. At some point, you are going to have to party up with people for something. You're going to have to work as a team with either friends or total strangers: and in that team your class will have a specific role. Really (and I could be wrong), I find it more productive and effective to focus on being the best at whatever your class does in a party than trying to solo everything. Soloing is a long, boring, tedious process (I know, I've soloed most of the game thus far).
Partying really helps lighten the load, and lets things move along faster. Instead of trying to solo in a game that is designed for co-op and party tactics, try to pick a class that has a role you like or are good at and work on developing your technique. If you're good enough at what you do, you won't have to look far for parties, so soloing becomes a moot point. Also, join a guild and ask your guildies if they'll help you with things. Nobody's going to eat you. You aren't going to get killed for asking people to help out. The worst thing anyone can do is say 'No'; which, in that case, all you have to do is ask someone else. With all the people in this game, you are bound to find at least one that either needs the same boss, or is willing to help you out.
Sorry for the long post, but those are my thoughts on the issue.