It should be what the couple is comfortable with. One of the things that really bothers me about modern relationships is the push by pro-equality people for relationships to be done their way and no other way. For example, a friend of mine who's a very intense feminist linked an article on Facebook that basically ran down women that want to take their husband's last name when they get married, how they don't have any independence and are accepting that they're owned by their husbands, etc. I hate my last name for my own reasons and want to get rid of it. I have no interest in making up my own last name because I hate the one I have and the connections associated with it. So when I get married, I want to take my husband's last name. That doesn't mean I'm property or not independent, and it's frustrating when I see things like that. It applies to how relationships are handled in general too; modern radical feminists have taken to looking down on anyone who chooses to be a housewife, because they feel that it's demeaning. However, the woman chose it herself for whatever reason. Maybe she likes housework, or is more comfortable not interacting with a workplace every day, or any host of other reasons, and it's irritating to see people that make that choice get looked down on for it. If you're happy and your partner is happy, and if you're making the choice for yourself, who are they to judge?
So that's my little rant on this. I believe the choice should be equal. Neither of the sides of the relationship should be subject to undue pressure from the other side to choose a certain lifestyle/relationship type, but they should decide freely together, even if it involves a 50s-style marriage. If that's what they want, leave them alone.