Rifles are "nice:wtf:" toys for grown ups, but they offer little assurance to survive a battle - they only fire, but they don't deflect bullets.
A mech is nice - my second choice of weapon, why 2.? You'll see... - it has a devastating firepower and extreme armor that crowns it the king of any battlefield.
Provided there's a battle - that's where nukes come into play...
(if anyone ever fires a strategic warhead I'm gonna swear to kill the responsible - serious. Hiroshima, Nagasaki - no more is ever to happen. I even consider banning tac-nukes as well.)Even that's not the ultimate answer however...
However if it were up to me I'd take this baby:

It's not my own unit though...
Nothing beats an S2 equiped, jet-black, Evangelion created form Lucifer's DNA strands, fitted with a flightsystem for mobility.