To be honest if your son is on the larger side, I would choose the Urban Jungle over the Swift. The Swift has a smaller seat, smaller wheels and a lower handle. I think the bigger Urban Jungle wheels would be better really.
I love the Bumbleride Indie and the Nipper - in fact I love the UJ too. I think all would serve your purpose well.
Have you looked at the Baby Jogger Elite and BOB Revolution's too?
The only reason I suggest these two is because I have a tall 4 year old, and I have been experimenting with which of all of these she looks most comfy in, and these last two have the best seating positons for her. I know your LO isn't 4 yet though, but I am looking to the future for the best pushchair for my nearly 3 year old and what will last the longest.
The Urban Jungle probably has the nicest feel to it and I love the basket, but the seat is on the shallow side which does seem to make a difference. The leg length is good.
The Nipper is probably my favourite to push and use - I love all the storage pockets, my DC loves sitting in it and always says she's cosy. However her knees are up to the bumper bar which is a shame because this is probably the one I would like the best to use - partly because its also light and feels smaller to use than the others.
The Elite comes out the best for me on every count really. Its heavier than the others but makes up for it by having super easy pop off wheels (reducing the weight) and then fold is smaller (and without wheels its tiny). But its got the best mix of a huge seat, with storage, with quick and small fold, with a huge hood, adjustable handlebar and is great to push.
The BOB I also love. The seat is HUGE for an older child. The fold is quick and easy - almost as fast as the Elite even though its 2 steps. Its easy to carry. The front wheel locks forwards for extra stability off road and its the only one with tracking. The handle is fixed though and I am not keen on the gap at the back of the seat (covered though).
The Bumbleride Indie is gorgeous to look at. I like the lift up calf rest for a sleeping child. On looks the Indie wins for me. Its great off road. The fold is a little more tricky - there's a knack to it and once you have it, its easy.
Oh and one more, have you looked at the TFK Joggster Twist. The seat on that is HUGE - probably the biggest seat I have seen. Its fab to push, has a handbrake for going downhill, its super comfy for the child. The fold is a bit bigger but its not as wide as say the Elite.
To be completely honest, all would be excellent. I think I would look more at the details eg whether fold is important, whether a huge hood eg the Elite would be a bonus over say the Nipper hood. Is light weight an advantage? Also look at your height - if you are smaller the Nipper may well suit (although its fine for taller people too) whereas the Bob having a fixed handle needs it to feel comfy for you. The TFK and ELite have handles which are horizontally on the tall side (but again have adjustability high and low).
Tough one really, but any would do the job.