Safety first, then scenery, then elevation changes and hills (I'm in Colorado Springs) But also variety. I have four routes in to work (but only three back because of a dangerous section not present on morning ride). My commute in the car is 6 miles, but three of my routes are almost 9 miles. One is only 7 miles, but not as pleasant or safe and I can't take it home as one bridge going home is not safe due to traffic. Along those four routes I may swing one or two blocks over to vary the scenery. And then I have three bikes I can rotate, my #1 commuter, a Charge Plug which is kind of a semi-touring bike, my old commuter, a Nishiki Blazer Mountian bike with street tires, and a Nishiki International12-speed road bike. They are all different enough to keep things interesting.

When commuting and also when riding to other parts of town I often choose a sleepy residential street over a bike lane on a major street just because it's quieter and more scenic.

Here are some videos of my commutes and other rides: