i have both a maclaren twin techno (side by side) and a graco tandam (front/back seats) ... TBH neither is easy to use on your own. the maclaren is heavy and difficult to open (dare i say impossible if you're on your own w baby). the graco is lighter, but again, you'll likely need both hands or at least a VERY strong arm to snap it open if you're on your own.
I was in a different situ tho; i have twins with an older child, so i needed a twin stroller, but... in hindsight, i'd probably have got around just as easy (in those early months) with the single stroller and one baby in a sling/carrier. But then my older child was 3+ when the twins were born. ... so was relatively easy to move with and was easily walking about ...
my advice ... try both out in the shop / before you buy ... try it single handed to see if you can do it with your toddler (or later on new baby) in hand...
the other positive w a single (and baby in a sling) is you'll get up and down escalators/stairs/elevators far easier ... ... you'd be surprised how difficult it is to travel w the twin strollers ... but that might all depend on where you live too
that all said, now that our twins are older, we use the strollers loads more... but again, rarely solo
also, see how easy/difficult the seats are to set .. the maclaren seats are set upright upon opening, and they're NOT easy to recline ... especially w a baby in hand (you basically need two hands to recline each seat). the graco tandam is easier here with one hand recline
there is a double available from 0/3 (can't remember the name) that "looked" easier, but it was for use 6mth up (doesn't lie flat)
best of luck!!!