Fenders (eg. Freddy Fenders): I say get the widest ones your bike can handle. Not just wide enough for whatever tires you have on your bike. That way, you can always put on wider tires if you want.So how do you like the air free tires today? I am interested in getting some. I have got to get fenders. I got away with not having them in Memphis but that won't fly here.
Airfree tires: I got the 20mm wide tires cuz I want fenders on my single-speed/commuter bike and the rear triangle looks rather tight, otherwise I would've gotten wider ones.
I like them a lot for the intended use -- zero chance of flat while commuting. I still don't understand the whole sluggish/harsh ride quality. The ride is plenty smooth, granted, I only ride steel so maybe it's different on AL?
I absolutely would not use these tires on a long road ride. My seven mile commute and tooling around town, perfect. I can take the pump off my bike, I can take patchkit/tubes out of my bags, I can leave the wrench at home (SS has bolts, not QR). As soon as I get around too it, I'll loctite the bolts down.
Commuting: I very much recommend 28-40mm airfree tires without hesistation. Do the 35-40mm tires if your bike can take them and fenders together. If I continue to commute through the winter, I'll splurge and re-evaluate (spend more money)
I wouldn't recommend them for any "serious" use.