I think the best way to decide is just to sit down with the 3 big ones (Stedman's, Dorland's, and Mosby). But I will give you my preference.
MOSBY all the way. First Dorland's is clearly inferior and harder to read than Stedman's so that is gone. Mosby has several advantages over Stedman's.
Mosby is cheaper (by quite a bit)
Mosby is easier to read
Mosby is a better made book (holds up better)
Mosby has pictures, good ones in color and lots of them
Mosby has everything you can find in Stedman's.
One note. There are two editions of Mosby's. One is red and one is blue. I believe the blue one has about 100 more pages (mostly reference stuff) and only costs about 4 bucks more. Definitiely get that edition.
I spent some time with all three and when done, even though Mosby was not one of the ones listed on our syllabus, myself and most of my friends opted for it anyways. Very good book.