I vent mine to the atmosphere. I use a MAP system so I don't have to worry about mismeasuring the air on shifts. I also have a custom intake pipe and it's just easier to not have to weld on another port.
The noise is quite noticeable at high boost shifts, but subtle just driving around town. The advantages to venting to the atmosphere is primarily getting rid of hot air and allowing fresh air into the intake pipe. Also there is probably less resistance to venting the air outside the pipe so the valve might be able to flow more.
Recirculating is supposed to keep the turbo spooling, but I'm suspicious that blowing air into a pipe with a turbo on one end and an open side on the other may not actually do a heck of a lot.
