It's pretty easy to rank them:
- Olympics RR comes first because Remco has won it and Pogi hasn't
- LBL comes second because Remco has won it twice
- Worlds RR comes third because Remco has won it
- MSR and PR come joint fourth because Pogi hasn't won it
- RVV comes fifth because Pogi has won it twice
- GdL comes sixth because Pogi has won it five times
All jokes aside, personally I'd definitely rank Olympics as a big win amongst Worlds and the Monuments and I do think I already held that position even before Remco won the Olympics.
For example, Van Avermaet won PR and the Olympics but (at least in Belgium) I think he will be remembered much more for his Olympic title (as 'Gouden Greg').
I also think that if Pogi doesn't manage to win an Olympics title before retirement and he had the option to trade one of his Monument wins (let's say one of his Lombardia wins) for an Olympics title, he wouldn't doubt it for a second.