I'm a big fan of energy weapons, but some kind of Heavy Machine Gun is an absolute must. Anything that shoots fast and plenty.
I used to be a dreadnaught main for most of the time I played FF, until I finally switched to Tigerclaw for the last few months of my playtime, after I got that sweet sweet soaring afterburner. Brute-forcing my way through enemy waves with the Mammoth was fun, but nothing would beat my Tigerclaw's infinite flight and 15m/s movement speed.
I never played any kind of Sniper (I always played with my brother, and he'd take on that role), and I did play medic and engineer sometimes, but I used their weapons quite rarely, so I don't care too much about those. Some kind of healing should exist, sure, but in FF I almost exclusively used skills (is that what they were called?) for that, and not really the gun - but then again, in terms of healing there was hardly anything but the Dragonfly. Some kind of sniper rifle and repair gun would also be nice... I guess. What I always wanted to take a stab at, but never got round to, was the Recluse with their pesky many poisons!
I'm pretty sure that would make a nice addition.
As for thermal weapons... I think a flamethrower would be really fun if done right, but I wasn't
that much of a fan of the Firecat's Thermal Cannon. What I'd really like to see would be something that fires lightning bolts.
Any I'd absolutely love any kind of music weapon, but... I imagine such a thing might not really fit into a massive planetary wargame.
When it comes to melee weapons, Firefall really didn't have much to offer. And I'm not too much of a fan, either, but if anything, I'd really like to see something like
"Aquila" from DmC... some kind of flying blades.
And a big axe or hammer might also be cool, I think... but I think there'd have to be something special in order for them to be able to seriously compete with ranged weapons.