Umbrella stroller, like the Mclaren - basically the fold is like the fold on an umbrella.
Be warned, lots of people on here rave about the fact that everyone will buy one by 1 year, in my experience, it really depends on your lifestyle, only one of my group of 'mummy friends' moved onto a Mclaren - I used the travel system/pram until DS was walking, and now DD is in the seat unit. I have used a Mclaren, but I found it hard to push, much more of a work out!
I would recommend getting a car seat you can put on the frame, makes life a lot easier, lots of buggies do this now.
For the pram, it really depends on your lifestyle, if you drive somewhere for 30 minutes, then walk around for an hour and drive back, you've hit the 2 hour window that DCs can be in a carseat, so you might need the option of having them lie flat.
For me, a rear facing buggy was important.
It comes down to how you think you'll live, if you are the sort of person who drives everywhere and doesn't do a lot of walking, then something cheap and cheerful then a mclaren would probably be fine, if you are likely to walk up and down hills for a few hours, you'll need something easier to push.
If you are going to be driving a lot, then something like the bugaboo bee would be perfect, it's rear facing, suitable from birth, folds in one piece and very small, and takes a car seat on it if you want. If you go somewhere like John Lewis, they sell them and they normally will take one out to the carpark so you can see if it fits in your boot.