my kids are 23 mos apart. and i didn't want to spend a fortune on a stroller b/c i didn't know how i'd use it..... luckily my girlfriend has 5 yr old twins and still had her duoglider.... so i borrowed that at first.
i liked the duoglider b/c the carrier can go in the back seat (where as the sit n stand it has to go in the front seat). but the duoglider is very heavy and my active two year old liked to get in and out... so then we went for the Sit N Stand Plus.
the Sit N Stand Plus - has a full second seat. most of the time i don't have the second seat on and my daughter is on the bench and my 10mo old is in the front. when we go out for long day trips (carnival, march of dimes walk etc...) i put on the full second seat. and move my 10 month old to the back b/c he'll be in the seat all the time, an and my 2.9 daughter goes in the front where she can get in and out.
my husband laughs at me b/c we have 2 kids and 4 strollers.... i have the garage space so it works... but you just never know what you'll need. i have the graco 1. metrolite that came with the carrier - use when we're at functions where i may need to lay my son down for a nap, at the park where my daughter is going to be running around anyways, and doesn't need a place to ride
2. the sit n stand plus - use for the mall
3. side by side jogger - borrowed, and only use for walks around the neighborhood
4. Chicco C5 stroller - folds nice and small like and umbrella stroller, but still has a basket, and shade
b/c i never know what i nead.... i'd definatley scour craigslist for things...