Go with tracker ...I have it on the Missus car with outsurance only cos it was a prerequisite. It self powered so they dont cut into any harness like the netstar unit. Had endless hassles with electronics on a netstar unit previously fitted to a co. vehicle as a result of them cutting into the harness.
Neither. In certain cars, they are not even allowed due to the way they plug into the wiring system. I know of a VW Scirocco with over R20k damage due to wiring issues after a Netstar / Tracker was installed.
My insurance required me to install a tracking device but VW said the warrantee will not cover any issues that may arise from wiring if I install Tracker or Netstar. At the end, for my own car, I went for Tracetec which is a small card (no wires) which they basically stick in the car somewhere. It is easier to hide (since there is no wires) and it is so small you can even hide it on a motorcycle or in a computer. I think I pay R80 per month.
P.S. I see etwylite mentions above that his Tracker is self-powered as well... so they've probably changed since the last time I checked.