Sean is okay. I like
Sean,
Shaun is alright too. I think
Shawn looks silly though.
I like Seana but I don't automatically pronounce it like
Sean + a, I'd say se-A-na.
I don't like
Shawna.
Shauna is okay. I like
Shana but that could be miskaten for
Shanna.
What about
Siana? I think it's pronounced the same way.