Same with me. Having a lot of fun with TF.
Not that I've got a decent amount of time in I definitely think the Chaingun with Accelerator is the best Titan weapon. When it gets going that thing absolutely wrecks other titans. I'm finding I get a lot more titan kills and assists with it, followed by the 40mm cannon and triple threat.
I used the 40MM for the Gen 2 challenge, but I hated it. I agree with the Chaingun and Accelerator, I like it. I haven't tried the other stuff yet, I'm sure the other gen requirements will make me.