I really can't get a good picture of my Shepards, but my male Shepard was meant to look like me but with a more military edge (short brown hair, brown eyes, a little facial hair). While that may not sound too different than Bioware's version, they looked rather different. Anyways, my female Shepard looked like a mix of Latin American and European American.
Regarding personality, my male Shepard was more laid back, very affectionate, and often took the Paragon route. My female Shepard was more up-tight (i.e. military-like), had a cold distance from her squad regardless of doing what needed to be done, and was a near even mix between Paragon and Renegade. Overall, my male Shepard was more of a mix between logic and emotion, while my female Shepard was duty-bound and rarely let emotions drive her decisions.
In the end, I preferred my male Shepard, but that was largely because he was really just me in the Mass Effect universe. My female Shepard was one that I was making up and putting very little of myself into.
Oh, and as far as class, goes, my male Shepard was an Engineer and my female Shepard was a Vanguard. That may also be why I preferred my male Shepard, since Engineer is my favorite class in the game.