What are you trying to improve? If you want to improve your speed, then the 5 minute intervals w/ 5 minutes of recovery will be ideal. If you want to improve repeatable, high intensity efforts, then the 1 minute intervals w/ 1 minute of recovery will be ideal. You won't really recover completely with the latter interval, and that's the basic idea.....

If you have your first race in 3 weeks, I'd start now....1 hard interval session per week. You won't be anywhere near peak condition for your first race, but it'll be better than nothing.