You're definitely not using Zaaed right if you think he sucks. He's not my favorite, but he packs a punch, and he can roll with it.
If you're a soldier, you can pretty much handle any fight on your own, using whatever tactic most appeals to you (since they're so versatile). With that in mind, I prefer to have squadmates that are either fun to have around for their commentary/dialogue triggers (Garrus, Legion) or who can take a licking and keep on ticking (Grunt, Zaaed). Grunt in particular can become borderline immortal depending on how you upgrade him, so he's a handy distraction to have while you gun down everything that's focusing on him. He's kind of a dull character, though. :-/
Soldier is the boringest class, though
No one should ever play Soldier
(4/5 players never play anything but Soldier)