Hellobee Boards

I don't have a 4 year old but a really tall 20 month old and we are looking at the Uppababy G-Link. A cheaper one might be the Graco sit and stand.

We love the bumbkeride indie twin. DS1 was 2.5 when DS2 was born. At age 4 and 17 months we still use it all the time and we will have a newborn in the fall. One side lays quite flat and it also comes with a car seat adapter for those very early days. We have the ride on board for if but don't use it that much yet. I'm sure we will when we have 3.

I'm a city mom with kids 22 months apart and opted not to buy a double until my youngest was about 1 (and I couldn't easily wear her anymore). I started out wearing the baby and pushing my two year old in our single stroller, and started to shift to sometimes letting the baby sit in the stroller while the oldest rode the buggy board once they were both old enough to use the regular seat. Around the one year mark, it became clear that my older daughter was NOT a walking kid (I know plenty who are!), and I got a double....but I do think with your age gap, it's very possible you really won't need the double.

I have a City Select double (tandem). I like it because I have the option to use it as a single (I leave one seat at DD1's school sometimes), and I can still attach a board to it if I want to move all the kids at once when baby #3 gets here. At nearly 4, DD1 is walking more, but still gets jealous/tired and sometimes wants to ride on longer outings. I also like the option of feeding them lunch on the go, and she can't eat on a board!

@winniebee: totally off topic but I'm a fellow bumblerider...did you know you can buy an updated recline mechanism/lever for your stroller? I got a new one and it is SOOOO much better than the dumb push button one. It makes an amazing stroller even better. I only found out because I called them regarding another service question.
just call customer service. its like 15 bucks including shipping. worth it (but I guess you need two for a double)

We did a ride on board on our stroller and my two were 3 years apart. We live in a city with no car, so we use the stroller daily. Depending on how big/heavy your older one is, you may not get too much use out of a double if she is close to the weight limit.

Kind of depends on your lifestyle. We live in a walking city and have the Britax B-Ready (I have a 9 month old and an almost 3 year old, so we currently have both regular seats), and unlike Septmomma12 above, we use it every single day, usually a few times a day.

Every time we leave the house, it's with that stroller. For my needs, it's been ideal. Neither girl has problems being in the bottom seat. My oldest can either sit in the lower seat, or she stands in the seat to play with little sister, whose upper seat is still turned backwards (if that makes sense). It's kind of like having a real double inline stroller and a single stroller with a buggy board, all in one.