Best - Any import
Worst - any domestic car.
(Yes, I am being sarcastic)
To be fair, even with the 'new' rejuvenated American auto industry (you know...except for Chrysler), I can't argue with a less severe generalization. Most of the American cars fall between 'competent' and bad. For most (jap) imports, 'competent' is the low end. Euros are wildcards.
But this is depending on how you define 'good' and 'bad.' I assume we're talking from an 'enthusiast' point of view- driving experience only. In my mind, though, I'm also thinking of price, reliability, build quality, ect. So I would generalize that for the money, you get a 'better' car with most japanese or korean models. But none of them are very fun to drive unless you start getting into their more expensive sport models (Infiniti G's, Hyundai Genesis, ect). Again, Mazda is the exception- Miatas are cheap and they also make the funnest FWD's, hands-down.
In comparison, you can get a powerful (hey, maybe even RWD) American car for not-that-much. You'll have more fun in a 20-30k Mustang that most 20-30k imports...still kinda handles like crap, though. :/
But I guess that's a bit OT/can of worms.
Really I just wanted to say that I forgot about Bimmers. I'm not a huge fan, but the sporty ones are a lot like the G37 I mentioned. The upside to the BMW's is they either have more power, or feel like it. The 300+ hp NA V6 in some G37's feels completely anemic compared to the, iirc, slightly lower-rated DI turbo I6 in the 335. That thing is a friggin' hoss.
And my butt-skidpad says the German will grip just a little longer. Steering also feels a little more precise and 'connected.'
That said, I must mention that German paddle shifts are retarded; Nissan does it right (big column-mounted paddles, up on right, down on left). For real manuals, BMW has better feeling clutches.
But yeah, for driving experience in a non-pipedream car (40-45k or less), I like the G for Japan and the 3-series for the Euros. Maybe Audi is some competition, but I've never driven a fast one. For the US...I just don't know. What has decent power, RWD, and doesn't throw handling out the window? Stock, that is. I mean, I can enjoy a Mustang stock, but to love it I'm sure I'd want some handling upgrades.