The Bi-Annual NEC shows are run by the National Caravan Council (NCC), while the EventCity-based shows are run by a private events company.
Not been to the Manchester show, but looking at the venue and exhibitor lists, I guess that the Birmingham shows are bigger. The October show takes over halls 6-20 (11 Halls in total - Hall 16 not used & 13/14/15 do not appear on the map) while the February Camping, Caravanning & Motorhome show, uses halls 1-5. It's still big, but also has tents and Static Caravans on show. I think the CCM show tends more populated by the domestic caravan/motorhome brands, whereas the MC Show also has Hobby, Dethleffs & the like.
This is a handy map of the October show: https://mcshow.co.uk/wp-content/uploads/2018/10/OCT-2018-FINAL-MASTER.pdf - I think its about a 2KM walk to do a loop of the show.