We have the Baby Trend Sit-n-Stand LX and it's worked great for our 3 year old and 10 month old. The front of the stroller can accommodate a child carrier straight from the car, so if your younger one is sleeping you don't need to wake him/her to get them into the stroller. Our 3yo daughter loves that she can either stand on the back or sit on the seat. We've taken it with us to Hawaii and to the Caribbean, and it's done a more than passable job with a decent amount of storage space underneath it. It folds much flatter than I initially expected and can easily be opened/closed with one hand. There's also a bar that "locks" it shut rather than some of the other models that have an internal spring/latch system. We've never had luck with those lasting very long.

One caveat: the wheels are smaller, probably 7"-8", and for that reason it's not the best choice on non-paved or non-grassy areas. It doesn't mind hills, but when we took it to an antique show with lots of gravel walkways I ended up running over to my in-laws house to grab our double jogger.