I'm gunna put myself out on a limb here and say that the spartans would likely(depending on numbers on each side)get pretty hammered by a battalion of Clone troopers. But that's the clone troopers, and those guys actually could fight and not die like it was in their job description.
However, *Storm* troopers are honesly pretty bloody well worthless, and if a single dude in a vest could stand there and make pot shots without getting killed, a guy in fully powered, cybernetically enhanced armor with impact plating, anti-plasma coatings and an energy sheild, who is more than capable of just picking them up and literally ripping them in half is pretty much going to single handedly destroy them.
If a spartan(maybe a 3 man squad) took on a large group of clone troops, especially the elite ones, then it would actually be a pretty intense fight I think, since they're both highly trained, and where raised on the same principles; plucked from youth, raised for the sole purpose of fighting, and assembled into a combat force.
It'd at that point mostly devolve down to field equipment. If the clone troopers have heavy close-vehicular support, the spartans might get their butts handed to them if they weren't careful, whereas if they didn't have the vehicular support, spartans would likely win due to being considreably faster and stronger, as well as have more durable gear.
I gotta tell you, I'd wanna see a fight between an elite Clone trooper squad and a spartan squad.
It would be awesome.