We have twins, the Mountain Buggy Duo, purchased from Mothers World, has been great. It is a bit bulky, so smaller cars it is hard to transport. We have 7mth old twins and it has had them transported around since they were born. Great to take on long walks, the shops or just to have around for those troublesome sleep times.
It will carry the twins until they are 4 or even 5 depending on weight. The individual shade hoods are great too. Storage is great and there are many accessories.