Gas or Electric...that is a good question.
And the answer is.....personal choice.
If you really need portability and are going to be filling many tanks at a remote location...go gas.
For me it is the Electric, and there are several factors that affect that answer. Mainly I don't need portability, I have my 100cuft tank(s) for that. Personally I prefer to run my compressor in a environmentally controlled area, such as my air-conditioned house or shop. With a gas model, you can't do that safely due to the exhaust. By using (air-condirioned) cooler air to begin with in the summer, there is less moisture that has to be removed. Low Temperature and low humidity air will help make your compressor last longer. There are two things that kill compressors, heat and moisture. Also I prefer to pump out Grade E or Grade D breathing air quality compressed air. Kinda works out, what is good for Scuba breathing air is also good for airguns. The more I can do to prevent moisture build up in my gun as well as particulate, the better. So I prefer the 220V electric with Grade D minimum filter cartridges in the filter tower on the Coltri MCH-6. If I was using this compressor for filling tanks for diving, I would also get it tested. Use to cost me around $35 to get a sample sent to the labs to be tested. Good insurance when diving and still not a bad idea for airguns....but a little over-kill.
I will also share a bit of wisdom that was passed down to me years ago on running scuba compressors that applies to us air-gunners as well.
When you are filling your tanks, don't shut off the compressor when it is running and pumping at high pressure....when your tank gets full, shut the valve on the tank, and open the drain valves on the water separators, while the compressor is still running. Allow the compressor to continue to run while the pressure of the compressor output drops down to less than around 50 Bar (approx 735 psi) or all the way to zero if you like. This will allow the compressor to do two things....cool down a little, as the only oil circulation on these lower end compressor units is a slap paddle system, and of course the fan is still running, but it also helps the reduce the load on the pistons and valve system before being shut down abruptly in mid-stroke. Happy diving and safe shooting.