redwood as i have posted elsewhere (fave subject) I would definitely recommned a b/board, esp with a 2.5yr old.
I have a 2 yr and a 22mth gap and both times used sling for 6months+ then buggyboard as needed. It's an excelletn thing as of course can be left at home altogether on short trips and just taken out on longer trips depending on how good a walker your older child is.
Agree with some you need to get the knack, it's not easy in eg high-heeled boots but much better than a huge double buggy. I would have thought that wd be a waste of space and money (tho you can get them cheap 2nd hand) with your age gap.
My 3 are now 5.4, 3.4 and 18months and we harldy ever use the board now for DD (the middle one, obviously!). This is mainly because if it is there she will use it (as s/one else says) when she could quite well walk. today for example she walked a really long way as she had no option!
(mean mummy)
popsycal by a one-handle buggy do you mean a 3-wheeler with a big push-bar thingy? If so that's what i've got with a buggyboard and it's fine. I worried a bit about DD not being able to stand between the handles, as she did with the Mclaren (RIP) but it's OK actually. the new stle buggyboard is adjustable to fit most pushchairs in fact.
Blimey i should be on commission here!!