To clarify, I didn't say tandems were only for people with infant carriers. I said it's BEST for those with infants.
For a sit and stand, I still highly recommend the Peg Perego Pliko 3/switch. They have a smaller footprint than the Joovy or Kolcraft SnS's. They are better made and more sturdy. They fully recline. Joovy and Kolcraft do not. They also have an almost complete black out sunshade and raincover zip on that's clear. The standing part is very comfy for older kids and doesn't get in the parent's way. My oldest is 7 and 50in tall and can still comfortably stand on the pliko while not interfering with the drivers. I'm only 5'4.5" and can easily push it with a child standing on the back.
For tandems where the kids can face each other, there are several out there. Kolcraft makes one. Fisher Price has a similar one. There are older Eddie Bauar's that do it. My personal fav is the Peg Perego Duette. The seats can go either way, face each other, face front, both face back or face away from each other. It was great with an infant and toddler. Seats fold completely flat so I had the back seat facing me in bassinet mode while my toddler was up front.
The downside to ALL switchable tandems is folding. None fold compact. They all require breakdown in pieces. Not idea AT ALL for busses.
I prefer strollers that are sturdy and solid, can accomadate a sleeping toddler/infant or a tired 5yr old, can be folded quickly and carried with one hand while having a baby on the hip. I also like strollers that can be steered with one hand in case I'm draggging a mouthy 7yr old to the sidelines lol.
I also like using 2 singles as opposed to a double. We've been doing this for about 3yrs now. My last double was an Aria Twin. I miss it.