Im englischen Omega-Forum gab es da mal eine Zusammenfassung von yinzerniner, einem der Experten dort. Dem ist eigentlich nichts hinzuzufügen.

Sapphire
Pros:
-Much harder material, scratches much less likely
-Almost all Speedy Pros with Sapphire crystal come with see-through exhibition caseback. Movement with exhibition casebacks is more decorated and has metal instead of plastic brake.
-Sapphire adds less distortion and is optically clearer than Hesalite
Cons:
-Almost all Speedy sapphire crystals exhibit the "milky ring" effect due to their design.
-Easier to chip and/or crack than Hesailite.
-Scratches that might arise are much harder to get out
-Replacement cost of crystal is much higher in the unlikely case you need to replace it
-More reflective
-Less distortion and a clearer crystal are not always preferred on the Speedy since its design is more vintage than modern.
-Slightly heavier on the wrist
-Speedy Pro model worn on moon didn't have Sapphire crystal, and they're not approved for flight by NASA
-Caseback inscription is incorrect ("First" vs "Only" watch worn on moon)
-Higher cost of entry (~15-20%), less supply

Hesalite
Pros:
-Hesalite crystal is more original to the watches worn on the moon, and all modern models with steel caseback are still flight-approved by NASA.
-Distortion and slight optical cloudiness gives dial a "warm" and/or vintage look
-Scratches can be polished out much easier
-Less reflective
-Models pre~1997 have the correct caseback inscription
-Replacement cost or crystal much lower
-Lower cost of entry, more supply
Cons:
-Picks up scratches easier
-More distortion and less optical clarity
-Most hesalite crystal models come with steel caseback. Only 3592/3572 come with exhibition caseback and decorated movement with metal brake.