Can't give you any experience of the other 2 but I have a 501 bought last December. Prior, I had a 201 and 301. My riding is 50/50 road and trail, mainly canal paths and the 201 and 301 suffered a lot of abuse, nowt broke, nowt fell off, I was impressed with their durability and splashed out on a 501.
I am seriously impressed with the 501, it's feels lighter and is way faster with it's better components, I would not have believed there could be such a vast improvement in a couple of hundred quid.
Niggles, I took off the Ergon pads and bar ends that I found uncomfy (See FOR SALE section)
and put on marathon puncture proof (I hope) tyres.
Some fantastic deals available if you want to do a bit of putting together yourself.