Hi paul
I have never used one of the flash car was things, as I have never found the need to be honest. I have never owed a black car, but my mate has a black M3 and he tells me that it is hard work. The best was to avoid water spots is just get pilling on the water, try never to let any area get dry and wash in the shade!
I use Meguiars Clay bar and soloution. It is very easy to do, although does take a while! It is very very good because it takes all service film, road grim, tar spots etc of the car before you wax/seal the paintwork, which is very important to get you a great finish.
I didn't waste my money on Autoglym as it is a very average product, so this is the steps I took on my new car when I got it. it is different when you have a used car as polishing would more than likely be required, this should not be needed on a brand new car!
Wash it thoroughly with with Meguairs NXT using a was mit! start at the top and work your way down, basic stuff i know, but make sure the last areas us wash are the most dirty(normally bottom of doors, side sills and rear of car) I wash single panels at a time and rise down.
Dry down fully using a dry town( much better than a chammy)
Clay bar the hole car to remove all gime and any service film(not much on a new car)
Seal the paint work using Meguairs Synthtic Sealant
Wax the car using P21S Carnauba Paste Wax-This is a high quality and is the best I have used so far on any of my cars! I have used Zymol products that cost £70 a tub and they are not as good as this in my opinion!
I then tend to wax my car once a month after this using the P21S
I use wax on my wheels that is also really good, but the name escapes me now, this helps brake dust sticking etc!
Hope this helps, this is the process I use and always get great results, it is very time consuming, but I think it is worth it! I hope this helps. I get quite a bit of the stuff from hear
www.cleanandshiny.co.ukNow before any one starts, i don't work for Meguiars and I do have a life

P.S if my spelling is bad in some area's I am sorry, I am at work and am dyslexic.