how many calories burned, what source do i trust?

vmessyness

today i did the elliptical at the gym for 3 miles/43 minutes (average heart rate 163). the machine told me i'd burned 436 calories. then i input my exercise into MFP and it told me i had burned 777 calories, which is a pretty huge difference. i never used to worry about this and went with the lower number, but recently i've been trying to eat back all my exercise calories. obviously i don't want to be over by 300 calories, but i also want to make sure i'm eating roughly the proper number of calories. i currently weigh 247 lbs. which estimate do you think is closest to what i actually burned?