I have used TurboLink for a few years now, we have other club members using Direct Scan. In my opinion, the advantages and disadvantages would be.
Advantages
-TurboLink
-Portability
-Boost Sensing
-Ease of use
Direct Scan
-Lots and lots of data
-Displayed BLM Grid
Disadvantages
TurboLink
-Not much data on a 11 second pass
-No displayed BLM grid
Direct Scan
-No boost data available
-Not as easily movable between cars
-Hook-up needs to be just right
Portability and boost sensing are big issues to me. I have had my TurboLink in 2 other GN's at the track this year without a problem. I also like having the boost record with the data file instead of relying on my memory.
I am also a fan of using ScanMaster 2 in addition to your laptop based scan tool. That way you can stay aware of the tuning parameters without having to bring out the laptop each time.
You really can't go wrong with either of the laptop based scan tools.