After playing MWLL for quite some time now, i find i change favorite variants every now and then. When 0.1.0 came out, i never touched a mech i was all about the Sulla B. I then went from BA only games to loving the AA Huit, the gauss/ppc Scat, the UAC10/ppc madcat, the CHLL Morrigu, the HL Puma, and most recently the Beatstick Shiva - which is my current favorite variant.
When i save enough money for one of these, i can literally clear the skies in 5 minutes if i dont get spammed by several Huits. It takes ONE shot to down anything thats airborne, even another shiva (if it exposes its large side to you). When that is done it can also be used well against ground forces, picking off wounded assets with one shot as they run away from battle.
Your current favorite variants and why you like them so much. Go.