you're essentially taking two overrated games and comparing them CSS wins because it scales better and has a lot more variety due to 3rd party mods and greater weapon choice... not to mention better physics
Depends what your into. CSS is more strategic and tactics orientated, Halo seems to be more like UT. Fast paced and randomness spraying.
Your actaully wrong about the 3rd party mods, There is way way more mods for halo then Css, There loads of communitys reloveved around modding maps for halo pc and not only that modding Halo xbox and halo 2 which do relate to modding halo pc By the way, Css is better
CS:S is by far better than Halo PC CS:S has little to no hackers, unlike Halo PC, also the gameplay is 10000 times better than Halo PC.