I went with CRM Europe and wouldn't hesitate to go with them again. I got my first airline job soon after.
They use a generic jet simulator set-up to replicate a Citatin bizjet which in my opinion is more than enough to get used to. Remember that the point of the MCC is to build your CRM, not learning how to fly a 737 or other complex jet!
It's all well and good paying £9K to do an MCC in a 737, and you might feel a tad more comfortable getting in to your Ryanair sim assessment if the cockpit looks familiar, but if your CRM skills are useless you'll still fail!
Personally I'd save the pennies, get quality CRM instruction, and then worry about your potential interviews afterwards. What if you never get invited to a Ryanair interview and (for example) Thomas Cook come along and stick you in an Airbus sim assessment but you did your MCC in a 737? It'll be totally different!