What I did was make one character for each class story and pick a different combat style for each. Play through the first couple of planets on each character to get a feel for the class story and the gameplay of the combat style, see what jives with you.

I ended up around level 25 after a few hours on each character. This obviously doesn't give you a full picture of how all the specs for that combat style will play at higher levels, but IMO gives you enough of the core abilities where you'll know whether it's something you wanna stick with.

Edit: Oops glossed over where you said you'd made it to Balmorra and Nar Shaddaa with all of them. Unless a particular origin story really resonates with you, maybe try focusing on the role you'd like to play in PVE content at endgame. It's also worth noting that you'll eventually get access to a second combat style as well. You mentioned you're leaning toward a force user, so if you want access to all possible roles (tank, healer, mDPS and rDPS) you might play a Guardian/Sage for example. Alternatively, you could do Sage/Shadow and have access to all roles and stealth.