MS2 and the AT3 are both good quiet AT tires.
IMO you're not going to see much if any mpg loss over ht tires if that's what you have now.
Toyo ATs are good, as are silent armor and Pro comp at.
If going with the same size, even mudders will only cost you about 1/2 mpg.
Get whichever is on sale or new takeoffs off of Craigslist IMO. Tires are too expensive anyway and tire warranty like most warranties is overrated. On the off chance you kill a tire you bought used, you've already saved enough on buying them to buy 1 or 2 new ones anyway.
And I'd probably jump to 265 75s. Those will still dual up without rubbing and are a much more common size. And it'll look a little better with bigger meats.