Thanks for your answer.
Once you get to Arx, the main weapon/armor traders would be Tarquin, Almira, and the few around the market area. Rings/amulets are also sold by a bunch other odd traders scattered around the city. And that's it.
So it is useless, according to you, to spend money before Arx island ? So, I come back to what I said, it is really a shame to get the best stuff in the very last moments of the game. You can not fully enjoy your stuff.
The real question here is not "who sells the best stuff", but "who sells WHAT kinds of stuff". Because they always sell stuff at your level. Pretty obvious.
My main is a Rogue, then Warfare Two-Handed DPS (Beast), Archer (Ifan) and Necromancer/Invoc (Lohse).