When DD3 was born last year, I had 3 girls 3 and under as well. I have 7 strollers--3 of them doubles, and 5 carriers, because I was always going to carry one, and I think I strategized every possible scenario I could think of until my very patient husband told me to stop researching!
There are things I love about each one, and things I hate. FWIW:
1) Zooper Tango--- not very common out there, but incredibly feature-heavy. It was our go-to in the van (we have a Sienna, as well, fits perfectly behind the back seats, with 1/3 of the space left to spare back there). The push isn't great, though it's fine on pavement. Will take a carseat without any attachments, fiddling, etc. (was a HUGE plus for us with the two littles 13 mo apart). The canopies can completely cover your kiddos---and I do mean completely! Baskets and storage galore, honestly, it's THE perfect stroller for us...except that it wasn't great on our horrid sidewalks in our last town. Here, I find I'm using it more often outside, too.
2) Baby Jogger City Mini Elite Double-- pushes like a dream, will handle any 3-4" sidewalk bumps with ease. Great canopies (granted, nothing like the Zooper), good storage. Doesn't fit in the Sienna unless we take one of the back seats out, so it's only our "around the neigborhood" stroller, unless we plan ahead and take out the back seat. Have to buy separate everything for it--car seat adapter, belly bars, cup holders, etc., etc. But again, a dream to push.
3) Baby Trend Sit 'N Stand-- Got this at Target this winter for $35, otherwise I had previously dismissed all Sit 'N Stands as too pricey for what they are. Honestly, I'm surprised at how much we use it now! It fits in the back of the van, though we do have to lay it down sideways (the Zooper will stand up, that's why it leaves some room in back). But we end up using it often as a triple stroller---1 yr old in front, 2 year old on the seat, and 4 yr old standing on the "stand" at the back. Probably not advised by Baby Trend
but it works for us, and is great for when you want to contain all 3 (ex: the 4 yr won't stop running around in a store so the 2 yr old wants to join her). For that reason, it's the one we've been leaving in the van on a regular basis this summer. It's not a "great" push, esp. with all 3 kids, lol, but it works. With the two littles it's fine. And it's great for walks when you don't really care if they walk or ride (zoo, park, etc), because then you let them do what they want. Our 2 and 4 yr olds just randomly ride for 2 min then hop off again, which is nice, not having to stop, buckle in/out, etc. every time they change their minds. It's got okay storage down below, but we have to be careful the girls aren't trying to ride in the storage compartment.
Sorry, I ramble when the girls are napping and I don't want to clean up lunch!