At the end of the day, you pay your money and do what works best for you.
There's been a fair bit of discussion over a number of threads lately. My take on it is something like this:
Portfolio used to get a lot of good reviews but there is some doubt as to the authenticity of some of them (fake accounts and punters associated closely with the agency). That said, there are Portfolio reviews from punters I believe to be credible.
A lot of WGs have left, and most of them don't have nice things to say about working there.
There have been accusations of poor treatment. Most of the ex Portfolio girls seemed to have suffered harassment, fake bookings etc since they left. There seems to be a difference of opinion on who is behind that.
There's also the whole silhouette escorts thing which seems to be a breakaway agency formed by one or more of the former employees.
Personally, I'm not into drama so I tend to go with Indies, but we can never really know what goes on outside the time we are with them.