We got a Joovy sit and stand extralight. It's great - space for the infant carrier, space for the toddler to sit or stand, really easy to open and close. The only thing is that it's big - probably won't fit in the trunk of a sedan. And expensive. And, honestly, we don't use it quite as much as I thought we would, because my three year old would rather walk than ride on the back. All that said, with the summer coming up, I'm glad to have it for trips to the park, mall, etc. If you are a fan of the sling/carrier, you might want to just stick with that for the beginning to see how much you need a stroller for two anyway. If you use it all the time, it's worth the investment, but they are pricey.
Sorry for my wishy-washy advice! If you do decide to go the stroller for two route, I do think the Joovy is a good one.