The only 2 mentioned I have experience with is spi (universal) and nason select. I'd choose the spi hands down.
I don't think nason select is all that bad either, always layed down nice for me and good clarity. Not sure of longterm, an honesty I haven't been able to see any of the cars I painted with them years down the road to see how well they held up. DId a repair on the brothers truck with spi, and if he doesn't trade it in the future (betting he will in a few years), might actually be able to see it after many years.
If using 496 and doing an overall, then probably want to use the slowest activator and reducer available or the 497. I've used the spot panel activator before painting a bike frame and a spot repair, and doing anything other then the smallest of areas with the spot activator can be a chore getting it on before its set up and your fighting being able to lay it down without any dry areas.
hood with 496 nason clear (did a spot repair, rest of the car is and hood was orginally marhyde universal)
carbon fibre hood with spi universal clear