Depends on your needs - I have a double mountain buggy, side by side Maclaren and a single Maclaren....
DD1 was 2.5 when DD2 was born. I walk at least once a day (usually 5km) and wanted to keep this up plus didn't want to load the kids in the car to go to the shops. Double stroller is good for shopping with the 2 and single is good for bubs alone or a short trip when DH is with us.
I was really keen to get out and be able to walk/park and shop with the 2 girls. I got amazing deals on both the doubles and plan on selling them on ebay once we have finished with them.
DD1 is 3 soon and still comfortably fits. Happy hunting!