12boy

I have a 3 speed 177% ratio SL-type Brompton with a 13 tooth sprocket and a 54 tooth chain ring which sometimes I ride with a single speed hub, 12/45. It has regular Schwalbe Marathons. I have a Xootr Swift with 100 lb Kenda Kwest and a 11/32 rear sprocket set up.I also just acquired a 53 cm Mercier Nano. it has a 42/52 chain ring and 12-25 cassette. Only ridden that for maybe 15 miles but have ridden thousands on the Brompton and a lot on the Swift, too. I'd have to say I like them all very much but there are some real differences...
The Brompton is the slowest and least comfortable on bumpy, irregular surfaces. It is not a lot slower, but is a bit. My hands get numb more quickly with the B although I have Ergon cork grips and cord-wrapped bullhorns. It shifts well and the 3 speeds are very good for this environment with some small hills and frequent 20 mph headwinds. It does very well hauling stuff with a large seat bag and a variety of front bags including the "shopping Basket" which is enormous. The bigger front bags add a lot of wind drag, though. It folds up very small and is really great for traveling with my wife and all her stuff in my Hyundai Elantra GT. Also good for bringing into the workplace, grocery stores etc. People here have a rep for unfriendliness to cyclists but I think they just find me amusing and I haven't had any problems. It has held up pretty well although I have gone through a few tires, chains and those 12 tooth sprockets. Living in Central WY I must order tires and tubes from the internet. I always enjoy riding it and since it does have fenders it is my go-to bike for rainy days. I think the B's long wheel base helps the ride a lot and the hing frame and fork hinge are as tight as they were when I got the bike..
My Swift is faster than the B since it is geared higher and the 20 inch tires transmit less road buzz. Easy to get tires and tubes. The components (hubs, headset and bottom bracket) have held up well. I never fold it so the hinge is not wearing at all. It is as comfortable as the Brompton and handles just as well. I replaced the rear wheel cones and they were fairly easy to order for my LBS. (I bought a new hub and also a complete front wheel for my Brompton since I couldn't find any cones by themselves.)
The Nano at 300 bucks and the shortest wheel base was a a pleasant surprise. Like the Swift I completely took it a part and greased the bottom bracket threads, headset and wheel bearings, as well as the seat post since they had barely any grease. The components (Seat post, hubs, crank arms and chainrings, headset and brakes (especially the brakes and levers)are cheap. I didn't even try the pedals or the saddle having SPDs and a Velo Orange leather saddle available. Having said all that, once properly lubed/adjusted every thing worked well so far. It is a lot of fun to ride and once I throw an 11-32 cassette on there it will be at least as fast as the Swift. Although bumps in the road cause my butt to leave the saddle, it has very little road buzz compared to the other two, much like my Surly Steamroller or my Holdsworth Special, both 700 C bikes with 35 mm tires. I don't have an accurate scale but it seems to be around 26-27 pounds, a little lighter than the Brompton and a little heavier than the Swift.
All three are nimble little bikes that are fun to ride. If I took off the wheels and seat post it would easily go in my car, same as the Swift, but not as compactly as the Brompton and would take more room in a a hotel room or an apartment. All three bikes, BTW have SPDs and Velo Orange model 6 saddles. As an entry level small wheel bike for 300 bucks, it is a sweet deal IMO, especially if you are just getting into small wheel biking. Like the Swift, which had so-so components, Hub, saddle and crank arms especially, I will enjoy upgrading it over time. Then again, I enjoy tinkering almost as much as riding.