I did Pilates with Rosemary MacDonald for a while before I was pregnant. She knows her stuff on the Pilates side of things and has some medical (nursing I think) background, but I eventually got frustrated with the 'organisational' side. I never felt I knew quite how many classes I'd paid for, or what exactly her rates were.
I did pregnancy yoga with Cheltenham Pilates and have now returned to their studio for barre workout. They seem to have good teachers and after Rosemary's one-woman in her own home setup, I appreciate the more formal set up of a busy studio. I know they've got a different preg yoga teacher now, but I'd trust whoever they had.
Some of my NCT mates went to Mary, and all I know about her is that they jokingly referred to her as Scary Mary! But they kept going and seemed to enjoy it really.