Hey Debbie,
My 1st daughter was 2 and 4 months when my second was born this past summer. We went with the combi side by side. I love it. However, My older daughter does not usually want to be in the stroller, so I end up using the single (I keep both strollers in the trunk), or I bring the double anyway because at one point or another she does want to ride. The double is good when it comes time for napping and we are out. If I had the sit and stand she wouldn't be able to take one. Also, my infant car seat doesn't fit in the stroller. It wasn't a problem for me though because the baby was born in the warmer months so I really didn't keep her in the infant seat (and I wanted her to be able to sleep through anything, so I like moving her around when she is sleeping). So now that I have been going on forever, i love my stroller, it was affordable, I can take it to the playgound, I can actually take it through some smooth trails in the woods, the baskets hold alot, the visors are pretty big for pretty decent sun coverage, I used it in the infant stage, it folds into thirds for better storage,and stands up when folded, there is a pocket for keys and etc. right on the back of the visor, it's not to heavy, fits through most doors and aisles, it has a extra piece of cloth under the seats that velcros around the front bar of the stroller to keep a infant nice and secure. Cons- you need two hands to open and close, and it has a draw string to lower the back of the seat, and you end up pushing it one side empty quite frequently. I think the Combi was the best choose, However if I had to chose a diffrent stroller it would be the sit and stand. I hope I have helped. A.