I'd say, once you've had jap, you never go back.
Jap cars do it for me every time - best balance of performance, reliability and gadgetry. The only thing they lack is the plush interiors and sometimes styling. I don't like Mercs because the build quality is quite poor. If you own a Merc, you want to own it under manufacturers warranty, cos you'll be taking it back a lot.
Audis are lovely, but they're overpriced. They make a great car, to the standard of other great cars, and then add 50% extra to the price. Beamers are nice solid cars, and I'd say if you can source one in the price range you're after, that's you best bet.
But personally, for me, Jap jap jap all the way.