For driving daily, the scanmaster is always there, and will give you the info you need most of the time.
It is only about the size of a ciggarette pack, so you can mount it where it is useful and leave it in the car.
The laptop based tools are better in that they record everything during a run, not just o2s and knock retard. They also display everything at once on the screen, plus minor things like P/N switch, AC switch, 3rd and 4th gear indicators, and turbolink can monitor boost with the sensing harness.
The main downside to DS and TL is that you carry around the laptop and some sort of powersupply. Also DS requires modifying the ECM in order to connect it up.
Get a scanmaster first. For daily driving you cant beat it. Then eventually get a computer based one to use at the track, or only when you need to. I have the s/m in the car 24/7 and I have TLink for the track and special tuning issues.