Slides are like guitars strings or picks. Not everyone will like the same thing. If you are in the UK you should check out Diamond bottlenecks. These are awesome slides
http://www.diamondbottlenecks.com/DB08/index.asp
Now as far as Rock slides are concerned..... well I have never used one but they look really good. I am not a big fan of metal slides in general. I prefer Glass or Porcelain. Out of all the metal slides I have used I prefer brass. Good sound and lots of sustain!