I would personally love an S5 over a 335iS because of the interior and overall looks--I think the S5, although arguably, looks much better than the Bimmer in person. Keep in mind that the S5 is mainly a rival against the regular 335i, to begin with. However, looking at the price, it fits both the i and iS categories. The iS will be better handling on a track, but the Quattro of the S5 will make it much better in weather conditions; it is also a bit more comfortable on the road, and more GT-feeling, so to say. If buying new, I'd personally go with an S5--or, within the same price range, a brand new, M-sport 335i sedan (F30), which is about faster than even the outgoing E92 iS. Both the current S5 and 335i are the outgoing models of their generation, so either wait for the new Audi or get a new 335i M-sport (it offers more horsepower over the standard F30). Unless, that is, if you're wanting the coupes. Test drive both rivals. That will be more than a thousand descriptive posts. Both cars are fantastic in their own regard, and both cars can and will be argued over each other. Here, of course, more people lean to the iS, because after all, this is a BimmerForum. Go to the Audi forum and you'll have vise versa. It's all about preference to which you value most. The iS is a sharp knife in what it does best, but the S5 holds its own respectable ground, thus leading to personal preference of each driver. I personally would be drooling all day over either or.