I've seen both Koko in Earls Court and Sue Lee in Croydon.
Only seen Koko once, but seen Sue Lee a handful of times going back 15 years or more now.
Depends what your age limit is and what you're looking for. But bear in mind Koko is now nearly 70 (those pics are old and very flattering). Sue Lee is 60, maybe late 50s? But she certainly looks younger than Koko.
Koko does a more specialist service. For an hour booking, you get an assisted shower, where she washes your cock and arsehole, then delivers a sensual body to body massage, including a deep rimming, OWO and, unasked for, reverse oral. Koko likes to bust a nut and will sit on your face and expect you to bring her off - and will show you how.
I had no problem with this and was happy to oblige as part of the experience, but bear in mind you are having a pensioner's vagina in your face. Something to consider: Koko's cunt muscles could probably take the top off a bottle of Budweiser. For a woman of her age, it's incredible. Clearly some serious pelvis floor exercises and tricks learned after decades in the game. We did have full sex, but it wasn't comfortable and I came in her mouth instead. But, like I said, she is an old woman.
Sue Lee's service is more route one. She will rim you, suck you off and let you come in her mouth, but also takes a penis better than Koko. Her vagina can accomodate more.
Good luck - and enjoy the experience, whichever one you choose.