Transsexual
Yikes! There are 42 girls just on EROS right now in SF....
http://www.eros-guide.com/sections/san_francisco_shemale_escorts.htm
I'd also do a search here on TER reviews, take a look at the EROS girls, and get back to us with a link to one or two girls for us to comment on.
Happy hunting! 
Mandy Mitchell. She's a big porn star now and her time is a little higher than the Eros average, but you get what you pay for!
She's a member of TER and pops into our forum here occasionally.
I don't know her personally other than exchanging a few e-mails in the distant past, but I've heard good things about her, and I've never ever heard anybody say anything negative about her.
I think you are better off paying a bit more knowing you will have a good time with a known girl, than taking your chances with an unknown.
Have fun,
TS Jamie