IS-F: makes a great noise and is a good looking car. Used, they hold their values quite well. Realistically; the seats are so-so and you feel a bit cramped. Everything looks ok, but when you're in one for a bit...it'll start to look and feel cheap. The gaps and materials used for things you can easily see are a step or 2 below a Cadillac. And you know what they say about once you see something...
M3: awesome seats and interior. Doesn't make the best noise but day-to-day, it's just as livable as a run of the mill 3-Series (no run-flats helps). Could be a fun car...but probably not in the way I'd like it to be. Driving slow cars fast is much more rewarding to me. I'd buy a 335is instead.
RS4: I love this car. Feels a lot faster than it really is...that's important. It feels faster and makes better noises than the older Shelby GT500s (and I'm not ******** you). Everything about it is wonderful, even the long throw shifter has its charm. Wish they made a wagon for the US. The only downside is that a quick heel-toe downshift will require you to wear flippers unless you are a Sasquatch. If that's the case;
goonie-goo-hoo
C63 AMG: I had a friend who owned one for 6mo and, according to him, it was a complete POS. The few times I was in it/drove it, I thought it made a good noise...and that's about it. Feels really 'dead' and over coddled. If, say, you were to break every speed law on the book by speeds that will land you in a mental hospital...the car will feel like it's going no more than 65mph or so. It didn't feel 'sporty' or 'performance' at all. Is it fast? Ya. But unless you have your eyes on the speedo you'd never know.
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If you have $60,000 or more burning a hole in your pocket and you want a car for nice sunny days that has a bit of presence to it...there's much better choices than the cars you've asked about.
