i think the only argument that can be made is the difference in the mil's which contributes to a "sloshy" factor. Some guys complain that they can't get good footing with boots on and refuse to surf the winter because of booties.
I would personally stay away from split toes because they are prone to leak in the split. Happened to me already twice, but you feel like you have better traction or footing in a split than a round toe. Also, try them on. Some brands run big and others run small.
I have a pair of 7mm, and if i'm putting booties on I might as well buy a pair that will get me through the winter. But hey if you have the money get 3's and 7's. I don't see any point in getting 3 pairs.
I will never buy a pair of 3mm boots again. I bought a pair of 3 mil split toes last year and they are not one bit warm. I had a pair before that and it was the same deal. The only thing I will buy from now on are 5 mils for right when I have to put boots on in the fall and sping, and 7 mils all winter.
5mil booties are the go to boot for almost any condition when you have to wear boots. 3 mils are a waste of money for mid-Atlantic surfing. 5 mils arnt that heavy either. Better to be warm than cold and the 5mils grip better than 3's I have the Oniel 5 mil split toe. They're good tl about 45 water then its time for 6 or 7s. My next boot will be a 6 or 7 round toe. heavier but worth the warmth. When your limbs are warm you are warm.