Personally, I would go for the Rat Jnr. over the Gen-X cockers. The main difference between them being that there are better parts you can buy for a cocker, whereas the Rat impulses are pretty damn good as they come.
I reccomend the impulse over the cocker. Smply due to the fact that they are almost as upgradable as the cocker (my impy's only stock part is the body) and you get the high ROF staright away, as opposed to shellling out $500 for an e-blade frame!