Plasma cutters don't have scratch start, think your getting confused with tig sets there alex. They have 2 types of startnig, HF and Pilot arc.
HF is just as it says on the tin, uses hf to start the arc - supposedly won't work on paint or rusted metal. Also might kill electronics etc...
Pilot arc uses a spring loaded 2 part electrode inside the torch head, the arc starts inside the torch using the lift-arc process (you can find out about this via google - quite simple) and is then transfered to the work piece when you hit the button. It will start and cut on paint/rust and doesn't use HF so less chance of interferance with the radio and killing ecu's etc...
Mate, I've got no experience with either, just relating what I have read up on... Personally, I'd get the bet machine you can justify and afford! And if that means you end up with pilot arc or HF, then so be it...