If you want a homebirth (and I fully expect you don't!) you'll need to get the one with the community team that covers your area. Apparently choice does not exist for this 
If you are Twickenham, St Margarets, Brentford, Hounslow your community team will be W Mid, but Richmond, Kew, East Sheen, Ham are Kingston even though you can have a hospital birth at either.
Fwiw I had DS at home under Kingston 3 years ago. The antenatal care was sub standard due to my v bad midwife. The birth and aftercare was good. This time round I am with Kingston again because I want another hb, but also because W Mid were terrible when I tried to register this time - did not return calls, did not answer the phone and I had to make a complaint about something and 12 weeks later neither midwifery matron or Director of Maternity Services has been in contact despite leaving messages on the answerphone for them. I also found switchboard could not connect me and kept cutting me off or directing me to a very stressed sounding labour ward.
Conversely all my appointments this time under Kingston which have been at Queen Mary's in Roehampton have been good (except for one epic wait due to someone else's emergency). I opted not to have the MW based at my GP surgery because she is the one who went AWAL and left me very ill and almost missed my anti-D injection.
So really it's much of a muchness but my recent experience suggests W Mid are very stretched and I have no wish to be in the middle of an department in crisis when I'm having my baby.