"Better" for what?
The Shaman would be the best choice for a tradeskilling character as the others are all useless melee.
For the magnificence of their surroundings and heritage the Vah Shir is the only choice.
Iksar spend their time in sewers dwelling on past glories. Trolls don't even have a home town anymore having been driven out by frogs
Oh? You wanted fastest levelling quickest to phat lewt?
No idea. I don't do "levelling".
Why not try them all starting with the one that seems best to you and then stick with the one that seems to be the most fun. You can always go back to the others if it seems to get stuck. After all "a change is as good as arrest"
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Wherever I go - there I am.