This whole thread is ridiculous, but it's easy to see who here has actual experience and who doesn't.
The vagina is not like an ear piercing, where as you put bigger things in to it it gets stretched and permanently distorted. When you fuck a girl, you're not feeling a tightness on you because you're deforming her skin, that's her muscle squeezing back on you. Realistically, the more a girl fucks the tighter she should be. If she hasn't fucked in a few days, it will take more work to get it loose enough to get in to and will be more sore afterwards, but that's no different than taking a week off of jogging and needing to warm up a little more first and feeling it more the next day.
Childbirth can certainly move things around, but I've slept with a couple women who had had children and they were almost too tight. I think women who have just had kids probably don't have sex as much for the first while (since they're getting up 3 times a night to change their babies), plus they're older, so I guess that could account for the muscle weakening up. The moms I was with had plenty of sex and were pretty active, so maybe that accounts for their tightness.
In summary, I'd take a confident, physically active, sexually adventurous woman any day