Cocker's are one of the most complicated and difficult to set up / time correctly. I would strongly suggest looking at something a bit more user friendly.
Dare I say it..........An Ion maybe?
They're actually ok to set up if you read the manual and are methodical BUT i do aree they can be a bit more time consuming than other guns. For a first marker that you just want to get out of the box and shoot paint, you MIGHT be better off getting something simpler.
The Proto Rail is a good starter marker that shares a number of features with it's big brothers - Proto Matrix 7 (PM7) and the DYE Matrix 7 (DM7). Check out
www.paintballwarehouse.co.uk and they'll have more info on there.
I think most people will agree though that you shouldn't just buy something cos one of us says it's good! Get along to a tournament and see what people are using. If you like the look of a particular gun ask the person using it to tell you more about it. Most people will be happy to talk you through their pride and joy! Whereabouts are you based?
The NSPL tournament series holds tournaments in Bristol, Newton Abbott, Dartford and Reading. The next Reading one is this weekend. If you're near to Reading check out
www.nspl.co.uk for more info.