Between the live wire, SCT XCal3 and the Chip?
Livewire supposedly gives real time readings but I have heard that its a good thought, just doesn't work enough to justify the money. The hand held Xcal3 can read all the OBD codes your car can throw and can datalog as well. The chip is the least expensive and you can buy a different changer to change tunes on the fly, but the shop I go to won't handle chips. If the connection points for whatever reason don't touch and the tune vanishes for a little bit thats bad news. Chips also will have to be reburned for every mod you do, the tuner you just tell them what you did and they can write a new tune for free.
Best bet and most common is the hand held tuner. SCT FTW