well, i can only tell you what i would do. your base training status, talents, weaknesses, etc. all determine what is the right training for you.

for me: i like the pyramid intervals. i've always had positive benefits from it - it's a cornerstone in my training. typically it goes like this:

1 minute on 1 minute off
2 min on, 2 min off
3 min on, 3 min off
4 min on, 4 min off
4 min on, 4 min off
3 min on, 3 min off
2 min on, 2 min off
1 min on, 1 min off

i do these as max effort intervals, so i'm basically going as hard as i can and then soft pedal in between. but, as i mentioned above, you may need to do some longer intervals as well: 3x10, 2x20, etc.

just remember to start off slowly. do intervals once a week for a while, then twice a week. i never go beyond two interval sessions a week. especially if i have a race that week.