Id back up what was said earlier,
Go out and try any and all markers you can get your mucky mitts on.
If you find a nice Impulse (for example) on the internet, Make sure youve tried an impulse (preferably that one if you can) before you commit to buying. That way if you dont agree with the marker (and everyone has pet hate markers) then you havent already wasted your money.
As for which marker to go for. Its purely budget dependant.
Second hand will bring better markers into range. But check who you are buying from.
If ya like cockers, always give DangerousBrian a shout, he's usually got something in the pipeline. But do check classifieds on this forum.
i am continually shocked at some of the prices some makers are sold for, due to the seller having their balls in a vice, with a female "other half" cranking it tighter.
If ya need any more help. give us a shout