>>96752387
For your setup, probably go with the medium frame. Your light frame isn't terrible but I think melee light frames need to be run with another melee frame of some kind since they run the risk of getting one shot on the way there + don't pack the same punch bigger frames can with their upgrades. Also with your team setup, having your spotter die will severely compromise your rail gunner, and they WILL die when when the light frame inevitably gets merc'd and then the pilot ejects at the feet of whoever they were slapping around.

The medium mech will likely be in cover (and not within slapping distance of an enemy mech) which gives the pilot a chance to eject and keep playing spotter for your team.