I have done EXTENSIVE homework on this.
Right now, for reasonably priced strollers, the only side-by-sides that take infant carriers are the Combi, the Peg Perego Aria 60/40, the Baby Jogger City Mini Double and the Zooper Tango. You can also add the Valco Lattitude 2 to that list as well as some double joggers, but a lot of them are heavy and unwieldy for everyday use.
IMO, the Peg is awful. I have the regular Aria Twin, and I hate it. It's hard to push, opens when it feels like it and not when you want it to, and is really disappointing.
The Combi has gotten good reviews, but I'm not in love with the padding - my kids are frequently annoyed by the padding in my single Combi and the double is constructed the same way. Plus, when I've test-drove the Combi with the kids in it, it felt a little flimsy.
The Zooper Tango is a wonderful stroller. It's everything the Aria Twin should be. Great storage, nice baskets, comfortable for the kids, great shocks. Same fold as the Aria so it doesn't take up any more space. IMO, the Zooper is just the better stroller.
The Baby Jogger is my favorite of this bunch. It's light, it folds easily and compactly, the kids are so comfortable, and it has a great look. I'm not in love with the only dark colors available - I worry that this might get hot and stuffy in the hotter months, but who knows? It's got a lot of benefits - great steering, good suspension, good storage. It's a little pricey, which has prevented me from purchasing it, but I would if I could.
The Valco is unproven - it's really new to the market, but Valco is a proven brand. It's the heaviest of this gropuing, which matters to some people. Test drive it, if you can.
Hope this helped. I will sing my usual song - Do not waste your money on a tandem!!! What a waste. If someone gives you one for free, like a hand-me-down or something, take it, but if you get one as a gift, return it and get something else.
Good luck!