ANR-20:
The ANR-20 sounds better, but is bigger and heavier. It's very comfortable,
though. Nice, soft padding, and not too heavy. Very "pro" looking with
all-black soft leatherette earpads and a 'high-tech' black matte finish
everywhere else. 

ANR-10:
The ANR-10 is lighter and smaller, but still sounds pretty good -- not as 
good as the ANR-20, but the ANR-10 is smaller, which you might like better.
Some may find the ANR-10 to be less comfortable than the ANR-20, as the
behind-the-head design can put some pressure behind your ears. However, 
some folks find the ANR-10's to be very comfy, so I think it depends on the
size/shape of the head. 

As for how they look, well... You'd look awfully funny riding a bicycle with
the ANR-20's on your head, as they are pretty large. The ANR-10's look like
many other portable headphones, so they wouldn't be as obtrusive. But
seriously, you shouldn't wear Noise Reduction headphones while riding a bike,
because you need to hear when a car is bearing down on you. 

In the end, the choice is yours. Both are really good. 
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