The best time of year for me is when I get up at dawn and start my commute to the frame shop... after I ride the 10km it takes to get out of the city I have another 40km of wide open roads and fresh air and if I don't stop for coffee at the midpoint can do this in under 2 hours.
From home to the midpoint is a net climb and the last 25km drops me back down very gradually while the ride home is just the opposite... when I hit the 25 km mark I am usually tired of what seems like an endless climb and can look down on my city and can really pick up the pace if I want to... can often maintain speeds close to 40kmh over that home stretch as it's a steeper grade.
Sometimes I sleep over if I end up working really late but on many weeks I will ride home and can only think that other people might spend an hour driving home in their car and spend a few hours glued to the television or hitting the gym to stay fit while I spend a few hours riding home.
I try and knock down a metric or century on the weekends so might ride as much as 700km in a week which gets me in great shape for touring.