Did you find the Spellslingers more positional based compared to Espers?
I read that somewhere. The Esper as a class didn't really grab me and I would prefer Spellslinger I think.

I really enjoyed the Engineer I tried, I liked having the bot that could hold agro for a few seconds. Engineers just felt a bit different from the usual MMORPG classes.

Next I'll try a melee tank and Medic healer.