If your a Mobile Pro? the air pack will be the best bet in the long run.

 

You're not comparing apples to apples. The welding arc on the TB325 is nicer than than 302 but if you wanted to do (very) light gouging or have a need for a big compressor, the 302 air pack is the way to go. Consider you get a warranty with the 325. The 302 might be old enough you don't have to worry about over filling the fuel tank. The newer non EFI Kohler engines that drain excess fuel back to the carb can be severely damaged if the fuel tank is over filled. It causes the cylinders to be washed down and will burn oil like it's going out of style. If it is an older version the price should come down some. If you don't need the compressor the TB325 EFI with Excel power will save a lot on fuel costs and have a longer lifespan. It will also be quieter unless you are burning large rods.