I didn't answer- because it depends on why you chose those two possibilities.
If your beer is underattenuated, and it's hard to aerate when you put the wort in the fermenter, you need the oxygen system. (I don't have one, but many people do).
If your beer is perfect, except a wee bit cloudy in the keg and you want it brilliantly clear, then the filter system is the better bet.
I bought an O2 system recently and hope it takes my beer from awesome to super mega awesome. Honestly, I'm a bit skeptical, but I bought it anyway.