we have done both, moved from village to mixed primary. Some thoughts:
Our village school was very small, and the main reason we moved was lack of friendship groups for ds. dd was ok, lovely group of 4 friends, but since we have moved, so have 2 others so the last friend is now isolated. I was governor, and was aware of many of the struggles the school had, due to its size. There were many advantages, but in the end I don't think they outweighed the struggles, especially the friendship issues.
I would not now send my kids to a school that had fewer than 15 in each year group (village primaries tend to have mixed classes)
Before we chose the mixed primary, we looked long and hard at its results and at how they challenged the top while supporting the bottom. They have a good record for this, so i was happy to send them, knowing that they have a good mix, socially, racially and academically. I think this is a good thing for my children and makes them better more rounded people.
BUT - ds has been in a class with a 'challenging child' I am not criticising the child or the school, who have worked hard to improve the situation for that child and ds class, but they really have had a long haul of disrupted education due to this child. He has now gone to a special school, and things have calmed down. But he is not the only one who is disruptive, and I know that ds class is probably the hardest in the school. They have chewed up and spat out 3 of their teachers in their 6 years at school. (been off with stress or left mid year)
dds class is great, no major issues, wide spread of children, etc
dd2 is in reception, delightful class, very mixed, delightful teacher.
If I had know ds class were like this, I would not have picked this school