You can't compare a doubles player to a singles player! You might be able to compare their respective acheivements at the end of their career but that's all you can do...
uh, what? If you are talking about Badminton skills, it's like apples and oranges. If you are talking about how cute they are, they both are. But "why"? I don't know. They just are.
Camilla Martin has won much more tournaments than Gail Emms. For this reason I would say Camilla Martin is more reputable. But just as others have mentioned, it's not fair to compare a singles player with a doubles player. Afterall, there is no telling whether Camilla Martin is a better doubles or mixed player than Gail Emms. I remember one year (I think it was 2002) where during the qualifying round in All England, Boesen Anders and Kenneth Jonassen were playing doubles, and they lost to Tam Lok Tin and Wong Tsz Yin from Hong Kong. It's not fair to way Wong Tsz Yin or Tam Lok Tin is better than Boesen Anders or Kenneth Jonassen.
This comparison isn't fair either : Camilla is at the end of her career, Gail isn't! Obviously Camilla has achieved more titles including one as world champion in 1999.