If you're using the race as training towards your IM, obviously go oly.

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res, non verba

When I do a sprint I can normally train right up to the race and then recover quickly, I can even run some more the evening after a sprint race.

When I do an Olympic distance race I need to rest up a little bit the day before and then I'm done afterwards.

If I was training for an IM and I was trying to get all the training in that I could to prep for that race, I would race sprints throughout the season beforehand since both have little to do with pacing for an IM.

If I really liked to Olympic distance over sprints then I would do Olympics.

In short, it doesn't really matter much, do what you like to do.

I am going to invent a rule....

The rule:
hard tempo efforts, and un-tapered races - are best at 1/4 the distance of the ultimate race goal.

Want a fast marathon?
Do lots of 10k tempo efforts.
10k untapped races.

Want a fast 13.1?
Do 5k tempo efforts + intervals.
5k untappered races

Want a fast 140.3?
Do mid distance tempos 40-60 minute runs, 1.5-2.5 hr bikes
Olympic Distance triathlons.

Want a fast 70.3?
Do short tempos 20-30 minute runs + intervals, 45 - 1.30 tempo bike sets
Race sprints.

That's actually not a bad school of thought. After an Oly you probably need rest enough to even take the next day completely off.

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I still lapped everyone on the couch!

Why this train of thought? Not disagreeing just wondering.

I usually do an easy spin on the bike the next day after a hard race, then take the day after that off.