Is this a serious question? If so, Borg, hands down, no contest whatsoever. Orbital bombardment could level the planet, they can scoop everything OFF the planet and dump it in sun if they want. Technologically and numerically the Borg are light years beyond Skynet.
If it isn's a serious question then "wtf y00 chattin' 'bout, Terminators is like WAY cooler than stoopid g33k tr3k hahahahahh i poke your mummy blargle spit spit spit" (disengage Troll mode)
Choose whichever answer you feel is appropriate and disregard the other.