First to get married - Rarity, as she's the one with the most interest in it. It's her dream to meet that perfect stallion and she won't rest until she does. The others don't seem like they're in any hurry to get hitched because they've displayed little interest in relationships of any kind. And come on, she's Rarity! No pony turns heads like she does. Any stallion would give their left hind leg to have Rarity, so it's just a matter of time.
First to have a foal - It's a toss-up between Applejack and Rarity, but I voted Applejack. Since Rarity is more likely to get married, she'll be in position to have a foal quicker than Applejack, but she has expressed very little interest in actually taking care of kids, as evidenced by Baby Cakes when she refused to babysit. I could easily see AJ wanting to have a foal not long after her marriage simply because of how important family is to her.
End up with the largest family - Applejack, no question about it. Family is extremely important to her, much more so than the others. She'll need to have fillies/colts who can grow up strong and help out with the farm, so I would expect AJ to be popping out quite a few babies. xP I'm sure Applejack would want to make up for the loss of her parents by having a new large family to love and take care of, and she'd definitely want to honor the memory of them by being the best mother she could possibly be.
Edited by Sugar Cube, 22 September 2013 - 08:51 PM.