What double stroller is better for 2 children: an in tandem style or a side by side seater? Need opinions from?

Side by side seater does take more room. If you have 1 child who can stand quite good you could check out the Joovy Caboose Stand On. The Chicco Cortina is also a great double stroller and has multiple configuration. If you want a stroller for a more active lifestyle you could check out the BOB Duallie, it's a bit on the expensive side but I've heard great talks about it.