What ever size you do decide on, DO NOT buy a reed type compressor, they don't last.
"Lifetime Lubricated" means 'When the unit fails- that's it's lifetime'.
Only get one that is oil-lubricated.
Invest in a quality, portable, piston-type, 22 to 30 gal.
I have an Ingersol-Rand like this:
I got it on CraigsList for $400.
Most compressors this size max out at 135psi.
If you step up to a stationary 60gal or larger, they are typically 175psi.
SCFM....larger is better. Any portable unit will be 5 to 8 scfm.
Your tools will dictate what scfm you will need.
I would stay away from no-name brands, as you don't know who made it, or where you can get parts.
If you think you will be using it to blow out irrigation lines, or for painting cars, (the above) compressor is too small. You will need a larger tank and more HP (horsepower).
I do use mine to blow out the irrigation system, but it takes forever.
I have to repeatedly open/close each zone (with compressor at max PSI) because there's not enough volume to this size. But with increased capacity, comes lack of portability.... then you'll be needing a lot of hose.
You'll need to give it a little maintenance, drain the water, change the oil, replace the air filter.
But a quality compressor will last YOUR lifetime.
To save some money, you can replace the factory air filter housing with one that holds a lower-cost element. A factory replacement air filter for mine was $15 to $20.
I replaced the housing with this one:
The replacement cartridges are less than $4.00 ....