Well, Halo wins to me.
First of all, the UNSC has an entire array of MAC cannons that would destroy anything lesser than the death star. The jedi might overwhelm a few SPARTANs, but remember, Anakin almost got killed by some mine droids (or something of the sort). The death star would be as strong as, if not weaker than the covenant high charity, their holy city. If they got desperate, the covenant could just release a bunch of dreadnoughts and be done with it.
If any of you guys know about halo 4, or know about the UNSC Infinity, which is 3.5 miles long, it could blow up a few star ships with some MAC rounds and the archer missile pods. The UNSC has already started a new SPARTAN IV program and has a ton of SPARTANs now. This being said, about 5 SPARTANs could defeat one jedi, and the jedi are very low in numbers.
If the empire joined, the Forerunners would come and let the Didact kill everybody, and outnumber the empire simply by releasing a crap ton of crawlers and knights, and the promethean knights would release watchers, and annihalate everything in the death star. If all else failed, the Forerunners would get every race into shield worlds and activate the halo array, which would leave everything dead in the galaxy except for the few remaining, uncommanded droids, and all the other races in the galaxy.