A.Choosing the center for examination
I would say London for the following reasons
1.Standards of marking is strictly followed by examiners.Trust me its not easy being an examiner.Examiners at RCOG have to justify at the end of the day "Why did they fail a candidate".So go ahead with London
2.All good courses are in London:
A.RCOG clinical part 3 course of osce circuits:MRCOG final preparation for part 3(16th to 20th april ,any 1 day) and MRCOG final preparation :Recap course on 11th May
B.Whipps cross course(http://www.wxmec.org.uk/MRCOG_OSCE.html)
C.Teal fenning course
I attended Teal Fenning.Whipps cross is very popular among docs working in London.I would suggest do RCOG course which is in april.If for some reason you cannot attend it so early,do the ones which are close to your exam in May.
3.London is a beautiful place.Not too cold in May.You don't want to miss seeing the spectacular Royal College building RCOG,London tower bridge and meeting me.This was on a lighter note
B.Type of visa
Standard visitor visa for 6 months on priority basis.Fill the form available on the link below.
Request RCOG via email to provide you an acknowledgement letter saying that you are appearing for part 3 exam in London in May 2018 for visa purposes