I ran the
ViAir "Ultra Duty" OBA system on my LJ for about three years. It was great. 200 psi and had a 2.5 gallon tank. It could run air tools if I wanted. The only downside was it was (relatively) slow compared to some other compressors on the market.
I now have an
ARB Max Performance Portable Air Supply. It's a lower air-pressure than the ViAir system, but it's twice the CFM. It's wicked fast. That's basically the trade-off, either you get high psi or high cfm, rarely both (
in the safe form factor at least).
As far as OBA vs. Portable, I've run both and both have their advantages and disadvantages. This year with the LJ being off-line it's been nice having the portable system because I can throw it in whatever vehicle I'm driving at the time. Where as if I was sticking to OBA I would be without air all year.
I've use the ViAir portable compressors and they're good. Same with ARB. Both companies make quality compressors. Just make sure you pay attention to the duty cycles. I highly highly highly recommend investing in one that is 100% duty cycle. You'll pay a little more, but they will last longer and be more reliable than something that is 50% or 33% duty cycle. Compressors, like all electrical devices, don't like to be overworked passed their duty cycle rating, so for me buy-once/cry-once and get the 100% duty cycle (
same goes for OBA; not all OBA systems are 100% dity cycle).