Because of our "sitting" life style I truly believe the key areas to focus on are shoulders, back, hips and hamstrings.
I do waaaay more mobility work than stretching and find it more beneficial. I do a 20 min set daily usually watching TV. But if i had to pick top bang for the buck for me are:
1. Worlds greatest stretch (ton of youtube videos)
2. scapula hangs - hand from chin bar for 5 seconds, then retract scapula and hang for 5 more seconds...keep alternating for 1 min
3. Back stroke arm motion while using a "peanut" up the spine. (you can buy or just ducktape two tennis balls together)
Honourable mentions - bird dogs, airplanes, pigeon pose, aductor activation (sit on floor and lift one straight leg, squeeze and hold 30 seconds)...