T.W.
I'd recommend the double stroller over the sit and stand. I think it's better to have the option of him being able to sit if he needs to or is tired, and when he see's the baby sitting in the stroller he'll probably want to also (if he's anything like my two that are 18 mo. apart...they like to copy one another). If my older son (3) wants to get out, I let him and he just walks along beside the stroller. I always bring the double stroller over the single, because otherwise I run the risk of the 3 year old having a meltdown because he can't ride in the stroller.
I bought a BabyTrend double jogger stroller and it's great for what I need it for, lots of places to store things. I wanted one but knew I wouldn't be using it a lot, so I bought it used off Craig's List and got a great deal. It's great to have when you need it.