In my experience gas is softer shooting, tougher to clean, dirtier (need more frequent cleanings) and less reliable. Inertia feels like more of a punch (although I have an M2 that is back on target faster than any gas I have owned), but way way WAY easier to take care of. It only make sense, the gas is not being recycled so everything stays withing the chamber/barrel (for the most part). Opposed to gas powered which re-route it to cycle the action and then vent out as much as they can. Many new ones claim to "self clean" but they ALL get gummed up. Don't get me wrong, any inertia will get gummed up too, it just takes a LOT longer because (again) nothing is being recycled. It is also only logical that a well built inertia will out last a well built gas, less moving/vulnerable parts == less broken parts == more shooting!
Good luck with whatever you choose.
J