Particular builds? Not really. I'm one of those all's-fair guys who figures it's on me to beat the other guy, and if I'm not equipped for the job then I'd best hope someone else on the team is. I've even piloted Streakcrows, though I actually prefer a mixed armament of Streaks and regular SRMs (
something like this), even if it's considered horribly, horribly non-optimal.
That said?
Spiders.
I cannot abide the existence of Spiders. I don't wade through rivers of lava to kill Spiders - I go far out of my way to ignore the existence of Spiders as thoroughly as I possibly can, because the awful little cackling gremlins are
counting on me wading through rivers of lava. They exist solely to drive the enemy into a state of mindless, easily preyed-upon fury. Their sole function in life is to
at you, as often as possible, in as unbearable a manner as possible, until you completely lose your cool and waste half the match chasing the goddamn things down, costing your team any chance at victory in the process.
They're not combat units.
They're not scouts.
They're not even 'Mechs.
They are elemental incarnations of pure, undiluted
jackassery, and I will ignore them as completely as I can until such time as their vile shenanery can no longer sway the match...at which point I will expend ammunition by the freighterload, overload my heat sinks until they burst, shed whatever armor I have to, in order to drive the armor-shod fist of my machine through the blackened, irredeemable heart of whatever twisted goblin has deemed it proper to pilot a Spider into combat.
&%^#. YOUR. SPIDERS.