Comfort: I think the AD700 would have the edge with cloth pads compared to pleather. The pleather isn't that nice on skin in the summer, and it squeaks against your glass frames (if you have glasses). That's the only advantage between the two. I find the 3D-Wing system to be very nice, with almost no clamping force.
Isolation: A700's isolation isn't great, but there's some. 20dB, maybe?
Fit: You shouldn't have a problem with them, unless you have a small head. For reference, my head's about a foot wide.
Sound quality: It's more of a matter with sound signature, and the difference between open and closed. If you compared the A700 to the MS1, you'd immediately see that the A700s mids are recessed in comparison, but bass is heavier and treble is brighter/more prominent. Soundstage would probably go to the AD700, and the A700 having some soundstage (I'd rate it at about "1 foot on either side of my head", where the MS1 is "inside my head almost completely").
You'll probably find the A700 more enjoyable for electronica (I find the bass kick and treble is essential for dance, whereas the mids don't need to be superb). On the other hand, I found the MS1 more enjoyable for anything involving vocals, rock, and instrumental music (ie. Baroque/Classical/etc.) because of the forward mids (lending strength to instruments and vocals), and midbass/forward presentation for electric guitars (and specifically, bass guitars. I like picking out bass lines for fun.). The AD700s might be more "limited" (don't think that they can't do it at all, just that they can't do it as well) to vocals and instrumental if the bass is as light as some people say it is. Ultimately, the difference is small, and probably wouldn't bother you any which way you go. You might notice "oh, that doesn't quite sound the same", or "man, there should be a bass drum right now", but it's not like you'll trash the headphones. You just might get a different pair instead.
Most of this is relative to each other; I'm sure the A700 is pretty light on bass already, but I've become accustomed to it and find it "just right" now.
You could also look at the Shure SRH440 and AT M50 as closed headphones, and the HD555, K240S and MS1 for open headphones.
Between the A700 and MS1, I find all my music needs covered at that price point. I prefer the A700 for gaming because of the sound stage and bass response.
And finally, take everything with a grain of salt, and realize the differences most people talk about are small (yet noticeable), and nowhere near night and day.
(Everytime there's an A700 thread, I feel the need to chime in. Maybe it is my duty as one of few (many) A700 owners.)
