They are both great resorts and if you do a forum search you will see a lot of different opinions as to which resort is nicer. It is a matter of personal preference, but you can't go wrong with either.
Very briefly, the main differences between them are the SC is newer, bigger, the villas are a little bigger, in room washer/dryer in 1 BR or larger villas, larger pool area with a great Lazy River, nice beach but more crowded because of larger resort and less palapas per keyed room than the OC. The SC is a high rise and views from some rooms are spectacular. OF, OS, OV and GV rooms.
The OC is a bit older, smaller property, 6 story buildings, OF and OV villas but palapas may block line of sight to water (not allowed with SC which is one of the reasons there are fewer palapas), smaller but quieter pool area, quieter beach (btw- the two resorts have adjacent beach areas), between the SC and the Marriott Stellaris so closer to the hotel, washer/dryers on floor but not in rooms.
The biggest difference is that the OC is quieter and the SC pool facilities are much nicer, IMHO; others will disagree and like the quieter pool better. The resorts are not sharing pool facilities and use wristbands to identify guests.