I think the 2 resorts are right on par with each other, although different vibes/styles. Price difference is really down to the EP - if they're important to you, booking Portofino will be cheaper than booking Sapphire & adding EP separately.
I feel like Portofino is more uniquely themed & less busy. Sapphire gets traffic from Cabana Bay & Aventura guests using the Sapphire boats. Sapphire is gorgeous & well themed, it's just a much more common theme.
Either is lovely - have fun!
(Also you may consider looking at AP rates for your dates; they're out for Oct. There are no blockout dates on the cheaper Seasonal AP in Oct so upgrading one person & booking an AP rate may well save you money. An AP rate would make a split stay cheaper, letting you try both resorts & have EP for part of your trip.)