iP4 sounds like the best bet in your situation. The 4S is a split-second faster opening apps in most scenarios, for the extra money that little "delay" on the iP4 doesn't bother me at all. Its still super quick. The camera is great, you'll love the led flash and HD video. The 1080P on the 4S? To me that only means the same video would take up more space. 720P looks great
The 1080p means better quality camera and video shots. The p in 1080p means ppi (camera). The more ppi, the better quality. The 4 and 4S have a big difference in camera quality.