I have DC that are 11 mos apart, so sort of like twins. I have a double (BJCCD) and I also have two singles (Britax Blink and Graco Ipo). I use the double when I have both kids by myself, but if I have DH or someone else with me I will use the singles so that we don't have to hear the DC argue over who is touching who, etc.
We also used the singles when we were at WDW which was so smart on our part! (I learned that here).
I really like have both combinations. There are some times that I only have one of my DC with me so the single is helpful then too.
SAHM to Pete and Repeat my "Irish Twins" - DD 12/06 and DS 11/07
Never argue with an idiot. He'll bring you down to his level, then beat you with experience.