Turbo XS HPBC hands down. I've tried quite a few others but none are as precise and as well made as the Turbo XS unit.

 

The GFB is easy as pie to adjust, you just use an allen key, no locknuts to deal with. It's also very tiny and because the nozzles are inline with each other so it's easy to mount. Here's my installation:



Also, it's a little noisy, you can hear a hiss coming from it at idle. I emailed the GFB folks and they said the noise was normal, you can see a small hole in the MBC where the air bleeds from.