Choosing versatallity
well the thief as a profession doesn’t really need to choose more than one weapon set. it rarely benefits from it anyway, so most of us just leave the bow on the second slot for all the utility it brings. that said, thief can choose various ways to achieve the same thing: negating damage and doing single target bursts. i feel it’s a bit of a false variety, since in the end all builds are very similar for purposes, but it’s still my main and i still like playing it over other classes.
ele is very rotation-based, but there’s also a lot of room to think when you should swap in/out of an attunement if you think you’ll need to go back to it in the immediate future for a defensive skill. probably has one of the highest skill ceilings in the game, and as long as you don’t try condi damage builds, there’s plenty to offer in all game modes.
engi probably has the most versatility, since that’s the theme of the class. you can go power, condi, both, or go tanky, or go support, and your “weapons” are exclusive to your profession. no one else gets to wield a flamethrower, for example. just be prepared to deal with hobosacks haunting your character’s back for the rest of your life.
I’d suggest Ele of the 3. All weapon options are viable in some part of the game and each have a very distinct playstyle. The Elementalist is also one of the strongest classes in the game and is wanted everywhere.