I used to sell car audio at the Good Guys, and all i know is, DON'T GET A SHITTY AMP. I havn't heard too much about Blaupunkt other than complaints from customers. I like anything Nakamichi, great quality stuff, so out of your 3 options, that sounds like the one i'd go for.

What i recommend though, is the JL Audio 300/4 . This is an awesome amp, very high quality, good sound, and tons of tweaking options. I've seen it for around 350 to 400. If you want an amp that'll last and sound great, the JL is the one to go with (IMHO).