Well? Mine's a tie between "Mmmm, pistol whip" and, after eating decades old Animal Crackers, "Mmmm, turbulent".
MMMMMMM...64 slices of American cheese... 64... 63... (flash forward to morning) 2... 1... Marge: Homer, have you been up all night eating cheese? Homer: I think I'm blind... and, of course... MMMMM...Forbidden Doughnut...
I don't think it was a "Mmmmmmmmm", but one of my all-time favorite Homer moments was when he couldn't throw away this monster submarine sandwich and got so sick from eating it (he had had it for over a couple of weeks) that he couldn't go with Bart and Lisa to Duff gardens. Marge: "Homer, are you still eating that sandwich?" Homer: (eating the sandwich) "No." and Homer: (looking at the sandwich) "Oh, this is all your fault!" (grabs the sandwich while Marge is looking on) "Oh, but I can't stay mad at you!" (gets ready to take a bite out of the half-black sandwich)
When Homer swallowed the plastic couple off the top of a wedding cake under the mistaken assumption that they were candy -- "Mmm...pointy"
My favourite Homer moment, which is not an 'mmmm', is when he's telling Lisa how to deal with her anger. I'm paraphrasing here: 'Just squash it all into a little ball deep inside and release it at an appropriate time. Like when Daddy hit the referee with the whisky bottle. {ingratiating fatherly tone} Remember that, honey? When Daddy hit the referee?'
mmmm, pistol whip definitely. 2nd hardest i've laughed on the simpson's in years. after that probably mmmm, caramel (as his kids stand tarred to him) b/c that was the first time i heard him do it. you know a show has a lot of classic moments when just the "mmmmm's" get a whole thread to themselves.