Hmm, depends what you're doing. Like a compressor bigger is usually better...but not always.
What I've learned:
Get brand name components. Many retailers like Harbor Freight and Northern tool simply assemble components and sell. This can be a good thing. Some "single brand" units hide what the unit consists off with facades and unusual configurations. BTW, I really don't care for the vertical shaft engine types....why? I don't know
As far as engines go Briggs or Honda would be my choice. For Briggs the IC or Vanguard series are awesome.
Good pump names are CAT, Giant, Annovi Reverbi etc
Keep in mind higher PSI IS NOT the only feature to shop for. An often overlooked factor is the GPM capability. More water throughput is better. Unless you're happy with cleaning a very small pattern at pressure.
Wether your washer pump has an unloder valve or not make sure the water is flowing through the pump (and out the wand) when the engine is running. Otherwise the valves (ceramic preffered) and other internal pump component will fail.
Make sure to get non-marking hose. It's a pain when you have a trail of blue or red to clean up.
Quick disconnects are worth their weight in gold.