My DD couldn't choose between history and RE. First history then changed to RE at the last minute. (BTW our school won't confirm choice and sometimes children have to do 2nd choices as the school can't always satisfy every combination)
Anyway being old, I thought RE was a bit of a soft subject but I've been very impressed with the content. She has studied Christianity and Islam. Included in these areas has been the role of women etc. The course has been particularly useful for giving a balanced view of Islam in these difficult times.
We are about to go through this with DS and having been through it once I am much less concerned. The school won't let them specialise too much - one MFL, one technology, one creative etc, but does allow for strengths so you could do 2 languages, but not 3. It makes sure there is a wide range - DS seems to choosing everything ending in studies
I'm hoping that's not possible either
To sum up I would say it doesn't matter -they are both good subjects.