I've seen them both and their reviews would confirm each range from above average to great providers. Personally, I would go with Sarah Brook. She seemed more real, not as caught up in the "act of making video" as Giselle seemed to be. Sarah seems to want you to enjoy yourself more, it was a bit more personal and less business like for me. Sarah's in better shape, I find her face more attractive, her cock is a bit bigger and she stays harder than Giselle.  

There's also compatibility and catching them in a good or open mood to take into consideration. I may have simply had better chemistry with Sarah and caught her in a better mood? I may go see Sarah again, I probably would not see Giselle again. That's solely based on so many other girls to see, I had a slightly better exp with Sarah and find her more attractive. It's a close call. With both of them sucking up to them, easy going communication and treating them like a princess can go a long way. I hope this helps!  

as good, cannot repeat or recommend.