Tac is probably the easiest to start out with. It’s what I run as my main Fed.

Engineer and Science need a bit more effort to use properly.

You can have a decent amount of characters, so there’s no issues starting a new character in a different profession to see what it’s like. (Also allowing you to have Federation and Klingon Captains.)

Also look for active promo codes. You can get a lot of good stuff with them.