I *LOVE* the Orbit Baby. Moves like a dream - they clearly put a lot of work into good engineering. It's also super-easy to fold and expand. They have great videos on their website showing how to fold and expand with one hand and one hip. It also has all the requisite bells and whistles: two cup holders, height-adjustable handles, under-stroller storage (that's a little small, but can be conveniently removed and toted around separately if you need to "valet park" the stroller).
I've only tried it so far with the infant seat but they also have a toddler seat that pops onto the same base.
It's expensive and relatively new, but if you have a chance to try one out, I think you'll really like it.