My (admittedly qualitative) experience, is that N2O oxidizes less than O2, although it's probably not as good as GP's suggestion to use Argon. It's mostly useful for finishing a bottle the day after without compromising on taste. I'm not sure how it might keep if you're hoping to save the wine for longer.

Argon might last for longer than one day, which is a plus! But I tend to finish the bottle within a day or two, so N2O works fine for me.

I've had good experiences with pumping out the air from the bottle with a wine saver vacuum pump and special bottle cap. Very effective solution, next to finishing the bottle.