I bought my iPhone 4S about two or three months ago. It came with iOS7 (running 7.1.2 now) and I must say that I am very pleased with it, everything is smooth and everything I need works. Not to mention it was a BIG step forward coming from a crappy Android phone.
Regarding iOS8, the vast majority of 4S users that have update to iOS8 complain about it, (slower and worse battery life). So until a newer update improves this and until I start reading 4S users being happy about it, I'm going to stick with iOS7. No need to risk having my good experience with the 4S go away.
Regarding iOS8, the vast majority of 4S users that have update to iOS8 complain about it, (slower and worse battery life). So until a newer update improves this and until I start reading 4S users being happy about it, I'm going to stick with iOS7. No need to risk having my good experience with the 4S go away.