[laminar]

I think it depends what you are trying to do:

1) Train for Max effort

2) Train for general apnea ability

If you want to train for a maximum effort, I would go with 3-5 reps at 95%-100% with lots of rest in between. No warm-up. With a buddy, of course.Then if you feel like it (your limbs should be noodles after this), do some cool-down lengths nice and slow.

If you want to train for general apnea ability, then lots of reps are probably good, with short recoveries, at about 75-85% of max. Even better would be to do it on a passive exhale (FRC).

Specificity is the key. If you want to train for maximum effort in dynamic, option one works well. But I would also spend a day or two a week, working on technique in easy distances (50m).

My 3 cents.

Pete