There are a range of factors, and to some extent it's a case of looking at each claim to work out the best solution. MCOL can be the fastest if you are pretty certain that BA will struggle to draw up a defence. But if BA are going to contest the case it can be currently a slow process due to the backlog in the court system at the moment. CEDR has advantages such as being free to submit cases and taking a hard line on "all reasonable measures". Those who don't live in the UK more-or-less have to use CEDR.

That's the short answer, it's a complex area and all sorts of reasons why one works and the other does not.