elkiedee, i have had loads of doubles as my first two were under 16m apart.
the best one i had was the mountain buggy double urban, i do go off-road alot inc on the beach and the other buggies i had just were no good. i sold mine last summer and i am looking to buy one again at the moment for the twins. they can take one/two or a double carrycot and one or two kiddyboards. its not much wider than my single mountain buggy urban. i like having the four wheels as its more stable than the three wheeled buggies.
the phil and ted is ok, i have had several versions over the years but my second hated being underneath as a baby so i sold it but bought one later on when she was older. swapping kids around when the bigger one wanted to get out was a pain and the back seat wasnt big enough for a big child. my SIL has had one for 4years and loves it for her two boys.
the jane powertwin was heavy and tipped easily. the m&p double was bad, i only used it a couple of times.
the ABC buggy with toddler seat is fantastic if you have an older toddler who doesnt need s good nap just a secure seat. my little boy loved being up above the hood and it was really stable.
the easylife twins or singles with a toddler seat are really heavy and trap your fingers when folding.
i havent had one myself but i know people with mothercare urban detors who cant fold them and they are heavy.
some people love the maclaren twins but they are not suitable for where i go walking.