Really depends on your budget? Bank on £250-£420 ish for a tried and trusted one.
EVOMS makes very good CAI and it costs around £300, ITG/VWR and REVO CAI's are around £400 each. Don't bother with the Forge Twintake or the cheap REVO or the AMD one. Some of those homemade ones look good too just make sure you buy the section that attaches to the turbo (from Forge) as the MAF sensor ideally needs to be in a certain place IIRC.
I've had the ITG Maxogen, the EVOMS and now have the latest REVO one. As mentioned, they're all good. EVOMS for
cha cha cha, ITG for a pronounced impression of Darth Vader's
whooosssssh diiisssssssshh and the REVO for something in the middle of the 2.