I think one of the P-hawks would be my choice. Being able to jump AND fire all the lasers every turn would be a pretty huge compared to what most intro-tech can do. The jumpy-hawk has the ability to stack on enough mods to make your opponent more likely ignore it because it is so much harder to land shots on with it's jump of 6. That ought to help keep it alive and paying back its investment.
The Thud, while it could fire all its weapons every turn, doesn't feel like it is gaining as much to me. If you have a target at short range, you could add in the large laser, but would you shoot the LRM's at them? Probably not. You could fling some at a secondary target, but staying in a good position to do that with a 4/6/0 mech is going to be a serious challenge. Also, this is likely to make the thud (which still has plenty of non-CASE ammo bins) an obvious priority target. It just feels like all you are getting is the ability to consistently add the large laser at short range, and maybe take more low-probability shots with the mediums.
The Archer already has a pretty good firing cycle for long-range, and once you run out of ammo, those extra sinks aren't going to be doing much. Sure, you could fire the rear lasers more, but they are still rear-mounted and terrible! You could also now LRM non-stop instead of needing to drop out a launcher every two turns, and still fire your arm lasers as well. Unfortunately, That would mean you are likely splitting targets again or firing at one target at a non-optimal range. I'm not in love with either option, even though it would be possible.
My choice would be the P-Hawk. Failing that, I'd probably throw doubles on the T-Bolt before the Archer, but I do admit that one of the Archer's big problems is emptying it's ammo bins before someone manages to shoot one of them, and doubles would help with that.