I like Halo more. The franchise has a better storyline and is much more entertaining than Gears of War. Also, I prefer a first person view over a third-person view. Halo's multiplayer is better as well, since the servers handle the lag much better.
gears of war beats halo hands down, it has a better multiplayer opotion, with the horde and the advantage of having the ability to play agains coms. halo lets itself down in the multiplayer option as u need either a live account or someone to play with. plus halo repeats itself
Halo 3's multiplayer turned me away from any future Halo game (Halo: Reach....just make a new series already Bungie).
GoW 1 was just awesome. The multiplayer gameplay was unorthodox, which is why I loved it. I bought GoW 2 but grew to hate it and I would rather blow the dust off my GoW 1 disc than play GoW 2.
I like them both alot. But Halo is one of the best games I have ever played. They both had great story lines, but I found the chief abit more like-able than the grumpy gears characters =p.
Also I prefered Halos multiplayer at the time. Maybe due to the fact its a FPS, but I did like the maps weapons etc more too.