The best training for fast endurance running: 2/4's (2 minutes running / 4 minutes walking or very slow jogging) > 3/4's > 4/4's > 2/2's > 3/2's > 3/1's > 3/0.5's > 3/0.1's... (And 1 minute runs are anerobic and for the most part you'd be better off just doing continous longer runs instead. Although if your rest period gets well under a minute, you may start getting some benefit from 1 minute runs beyond a finishing kick.)

Basically run just long enough that it's mainly aerobic. And rest long enough that you're as close to completely recuperated as you've got the time to get.

The whole point of intervals is to spend more time running at or faster than race pace while still running aerobically. Shorter than 2 minutes and the running becomes primarily anerobic. Longer rest periods mean more time spent running faster, (provided you have the time for a longer workout). Furthermore no matter how good a shape you're in, the aerobic system takes longer to recuperate, thus as your running intervals get longer, you really need much longer rest periods to ensure each successive run is still at a good fast pace.

Otherwise, what's the point of even bothering doing intervals? Why do them in a way where you do less fast aerobic running?

And 2/2's > 3/2's > 4/2's etc, etc because provided it's still somewhat aerobic, faster running is just better. As you slow down your stride changes such that you're not even exercising all the muscles that you would need in order to run fast.

Short very fast runs with plenty of rest in between. That's how you should actually do intervals. The limiting factors are how much time you have and how much your joints can handle. (And how tired you are from inadequate recovery from your "recovery" runs.)