RUNNING: What is your favorite speed workout?

Question

I have two. I like to run 800's at 5k pace, (recover 400) about 6 times.

Or, I find a sort of busy street and stay on the sidewalk, whenever a car passes me, I get up to 5k pace, when ever another car passes, I can recover. This street is about a mile long.

Answer 1

I have two -
on a 400m track, sprint one lap then run at 7:30 pace for 3 laps

or theres a nice hill near my home, I run up, then jog down. Repeat until tired.

Answer 2

I like a good fast workout on a crosstrainer. The challenge is to see how many miles I can do in an hour.

Answer 3

100 metres