It would be great to know if there are any specific ones you'd recommend based on your experience looking at their websites. Also, do you have any tips on how to find a good, trustworthy agency?

I always trust them based on the feedbacks of their girls so you need to do a little reading lol. Passion VIP is pretty good one. 

Escortrankings is good they have a lot of girls and you can see their profiles if it's verified or not. 

Manchester Pin Ups is a good one too

I don't care about the agency, if I like the girl I'll definitely book her regardless of the agency she's in. 

 Deluxe Birmingham Escorts, I booked twice from their agencies, and both time I had great time 

Booked on from ER the other day. I will write my story in detail on Escort Reviews :p