Hospital gown. All the way. I can't understand what you think would make it uncomfortable? They're very "worn" and usually soft, have snaps at the shoulders to make for easy breast access, and are completely open in the back, meaning that you can lift it up or arrange in whatever way is comfortable. Plus, if it gets soiled (or should I say WHEN it gets soiled), you don't have to bother with it. That's the hospital's job.
A sports bra sounds horribly restrictive to me, and a skirt will not be realistic during labor and delivery. Doubtful that the hospital would allow a skirt or wrap that does not allow easy access to the vag.
I've found hospital gowns to be the most uncomfortable article of clothing I have ever had to wear (a total of twelve days combining my hospital stays the past two years) I hate that they open in the back and I always have to cover my butt when I get up, are all one size (Not everyone is an extra large) and the strings to tie them never line up right, and no their not soft at all in my experience.
I was actually thinking a sports bra and skirt would be great for delivery I hate feeling like my girls are free to bounce around as they please, and something short and non restrictive kinda like a tennis skirt would be perfect just enough to cover my butt cheeks and allows plenty of movement AND easy access to the vag!
Anyways my hospital allows us to bring something comfortable to wear during delivery which I'm glad! I found a couple different gowns that are short, loose, and have buttons down the front so I can breastfeed easily. And they were cheap enough that if and when they get ruined I don't mind disposing of them afterward.