The people who made Gears of War, Epic, have been making shooters for a long long time. Bungie has been making them for a while as well, but they don't have as many in their portfolio as Epic would.

They're both quite different games, and Halo is diverse enough to have an easy mode and a very very hard mode for the single player. Legendary on Halo is harder than Insane on GOW. If Halo used the cover dynamic, it would be a *very* different game.

Still, right now I can't choose fairly between the two :P I'll give Gears of War series a couple more years, because right now Halo would win on epic nostalgia. 16 player matches every week at my college, can't quite top that yet.