I've no experience of using Agencies, but, as with many other things in life, I don't think you can generalise about Indies.
Of the 7 Indies I've seen so far this year, there are:
two I'll never see again [one of them has since retired but I wouldn't have been going back there
one who I doubt I'll bother going back to [she was okay, but nothing special];
two who I'll see from time to time [maybe as a Plan "B", if Plan "A" falls through for any reason]; and
Incidentally, I'm writing here about British MILFs [aged 39 and upwards in Pro$$ie-years] and I'm not sure if there are many Agencies providing the species.