I just flew delta and it was horrible. Stay away from the newer airplanes as they have accessories that are in bad places for larger people. I actually had to get a whole bunch of pillows to pad the seat up to get the radio controls out of my leg on the 5 hour flight from Atlanta. It was singularily the worst flight I have ever had.
I did have a good friend who travelled for work and is a big guy himself recommend the older airplanes. Boeing 737-300's are good since they still have wider seats without the frills. Also, do not make the mistake I did. I requested an emergency exit row since in addition to my waist line, I am also 6'4" tall, to the extra legroom would be nice. It turns out that you cannot raise the seat arms on the emergency exit rows for some stupid reason.
I wish you luck!
Dave