"but now I'm stuck on a WG or HG..."
- Wow dude, I hope you can find some anti-superglue.
Jokes aside,
"I'm wondering about service side of things? Any advantages of either or..?"
- You dont seem to be a very experienced mongerer by asking this question. The service you get from a working girl varies mainly from the influence of the working girl's tiredness level, chemistry with you, your looks, duration of booking, her attitude, personality etc etc so much that you are just as likely to have "advantages" with a WG over a HG as much as a HG over a WG.