Another thing to consider is that any class poll tends to be led by the Big 4. So the Wizard being on top, not a surprise - Tier 1, Big 4. That any of the Big 4 didn't make the top is an indication they're somehow lacking.
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Those were popularity, not any sense of 'best,' though. Yeah, a lot of Beyonders roll up a Fighter named Bob at some point.
I play fighters regularly. I have yet to name one Bob, however. ;-)
I would point out fighters have been holding a steady 4th place on this poll even if rogues, clerics, and warlocks are close to them. The rest of the "big 4" traditional classes still represent. They just aren't part of the 3 break away classes we see.
I'm not surprised about wizards and bards up there. Versatility is valued and that they have.