I have no idea why Mac's are so expensive. Linux have the same kind of chip as Mac and I don't think Linux is that expensive.
The best Macintosh is the Quadra IMHO.
I assume you mean the best Mac. That would be the 12-Core Mac Pro. Running at 2.93GHz with about 12GB RAM, the Machine is a beast. Well worth the Money.
We had a Mac Pro here at work getting prepped for a client. It was pretty cool.
But in all honesty, just build a PC and get OSX. It's the exact same thing.