I have a 4S. It's a good smartphone and smaller than its successor, which I like. The display quality is fantastic. I see no reason whatsoever to switch to the iPhone 5 as it really isn't much of an improvement (imo), except that it is lighter, reportedly has an even sharper display (though I am not sure how visible that really is), a larger screen, more RAM, and LTE capabilities, all things I wouldn't be able to take advantage of, anyway.
In my view, you really can't go wrong with the 4S unless you need the latest and greatest. Though, if you need the greatest, then you might want to take into account other models by other manufacturers as well, such as the Samsung Galaxy S III, the Nexus 4, the HTC One X+, the Nokia Lumia 920, and some others. There are so many options to choose from. In the end, I'd test which Operating System you feel most comfortable with because that is the biggest difference. In terms of quality, the newer smartphones are all pretty much on par.