Should I buy Dead Space 2 or 1 (xbox360)?

I was thinking of getting Red Faction: Armageddon or Dead Space 2. I think I decided on Dead Space 2, but I was wondering should I buy the first one instead? Note: I'm only planning on buying ONE game, so I'm not going to buy the 2nd if I buy the 1st. Or should I just get Red Faction Armageddon? The destructible objects/ repair ability/ gravity gun seems absolutely amazing ( not to mention the mr toots weapon ha) but both Dead Space games have higher ratings on metacritic. Also, the foam finger in DS2 is pretty awesome ha.