I think the biggest variation in the courses is whether it's online or in the classroom. I've taught both and really prefer to interact in person if possible, I think you can get more across and deal with more individual questions - also the class sizes are smaller in the classroom courses. Obviously I think all my own products and classes are better, they are created because I saw a need for high quality content and I am happy with what I produce!
London courses are unlikely just because people come from all over the UK/Europe and here in Leeds I have no costs for myself, and a training partner that I'm already working with which keeps my financial risks quite small. Travel and accommodation in Leeds are cheap (we start later on the first day of training to cater for those who need to travel) so it keeps the costs down, both for the course and the total cost of sending someone. I do teach ZCE in London fairly regularly but I do that for specific clients where I work with their whole team.
Whichever option you choose, I wish you luck!