Mass Effect has two leads, Mark Meer and Jennifer Hale, but you’ll only hear one of them as Commander Shepard per playthrough. According to player stats, most people play as a guy, meaning Mark Meer is their Shepard throughout the trilogy.
However, Meer encourages players to give FemShep a go - purely so they can enjoy the performance of his co-star, Hale. Speaking with PC Gamer, Meer says that he’s a huge fan of her work, and doesn’t have any problem with players choosing to only play as FemShep because of her performance.
I’ve done playthroughs as both. I think they both have excellent voice acting. But I think the character of Shepard as Earth’s military golden boy/girl works better with the standard military jarhead looking guy. IMO he embodies the generic “John Masseffect” energy better.
It’s funny because the games do let you customize the appearance, race, and hairstyle of Shephard, but to me he will always be that default settings buzzcut guy with a fivehead and big jaw.