This is the toughest poll I've seen here thus far. I listen to Abbey Road at least once a week and it is in my top five albums. I haven't listened to DSOTM in its entirety in over a year. Although I used to listen to it all the time, it did grow a little tiresome. That's never happened with Abbey Road.
... wow! That's a huge contrast. You're talking about two bands that sound completely different from each other. That's like comparing apples to bananas. However if I really had to choose, without a doubt it would be Dark Side of the Moon.