If you are chasing big power then go for an ebc. If you are only going for mild mods then you can just stick with a bleed valve.
In my opinion the ebc( i have profec B II) is much better than a bleed valve.
The bleed valve would spike on my setup ( Had turbosmart dual stage). It was good at holding up to 12psi then after that the boost would spike.
Also with the ebc you can adjust the gain setting and start boost setting. This will let your boost hold more steady, and also make boost come on earlier. rather than a bleed valve which you can only adjust how much it will bleed.
This is from my experience and my recommendation is if you got the cash go the ebc. I've only used Profec B II so i can't comment on other ebc's.
If you got stock turbo and plan to keep it stock, then a bleed valve will be fine. If you are going for aftermarket turbo, then get the EBC.
Hope that helps.