I would give the nod to red faction. To be honest, I was never really interested in either but after playing both demos I'm more swayed to RF. Infamous, despite it's high polish, just feels too... "been there done that". I feel like I've played this game so many times before, and while it probably handles everything better than those other games I'm just not as excited about it as everyone else is.
Red Faction also gave me the same concerns, but the geo-modding really added something fresh and fun. There are so many strategies and tricks you can use by destroying your surroundings. Making quick getaways by sledging through the walls, destroying the enemy's cover(as they likewise do to your own), toppling buildings by taking out their supports, there are some really creative things you can do here. I'm not very confident that the game will work well with the whole "open world" experience, but it was still pretty damn fun. I'm going to rent and go from there on this one.