I also have to vote for the Baby Jogger City Mini GT. I've had a lot of strollers and this is my absolute favourite. It is very good on trails and folds up so easily. Not as tiny as an umbrella but much more comfortable and folds up nice and flat so you can easily fit it in the car, on a bus, etc. Being able to fold it with one hand is brilliant. Not as great going over logs or big rocks as something with larger wheels but larger wheels = larger fold (much larger in most cases). I find the BJCMGT wheels go just about anywhere.
They are about mid-range in terms of cost but have been available for 2 years now I think so used ones are probably starting to come available.
We also have the stand-up board that goes behind it and, though it's not as good for my posture as the Phil & Teds or Uppa Vista models (yes, I've had both of those too!), it is pretty decent. DS1 usually sits rather than stands on it.
Happy mumma to my boys Henny Tom (Nov 30, 2008), Arlo Odie (Oct 5, 2010), and baby SISTER! due mid-Dec 2014.