How olds you car? If its fairly new then personally I wouldnt bother polishing it for a while... or at the most use an extremely fine polish. So far i have only used a very fine cleaner/polish on mine but I have also bought a very fine finishing polish...
Instead use a wax. I have tried the Meguirs NXT wax and found that the finish looks very smeared. dont know if its me coz Val swears by it.... guess he must have plenty of practice .
I have just bought some P21s, only used it on the bonnet and it seems very good... better than meguirs, but it should be at $32.
Chris demonstrated the Meguirs quick detailing wax at the JAE.. seemed pretty good and extremely fast to apply.
I am going to be using Meguirs 1st then finishing off with the P21s...
I had supaguard on my previous car and my dad had it on this current. It was ok for a while, but wasnt impressed.