I'd go for four mediums
Wolverine 6M Good armor, mobile, solid weapons, and heat disapation
Kintaro 18 Good armor, solid speed, nasty weapons (inferno's [rockon]), runs hot though
Crab Good armor, solid speed, good weapons, and heat disapation
Dervish Good speed, mobility, long range weapons, and can defend itself up close
Not optimized but should work very well together. :)