There is only a 1/2" size difference with the adult sizes of the fish. Not a terrible difference considering the pygmys have been known to get just as large. True juliis are hard to find but the false julii (or 3 lined cory) still only reach 1.5" Personality wise there isn't much difference that I am aware of. They are both active bottom dwellers, although the pygmys do frequent the mid level of the tank.
King PK Wasabi; HMPK Frostini; 5 CT Bettas Jewel, Shimmer, Opal, Scarlette (aka Ms. Piggy), Pixie; 1 SD Neptune; 1 HM Gypsy; 1 DTHM Pebbles; 4 Orange Von Rio Flame Tetras, 5 Bleeding Heart Tetras, 4 Harlequin Rasboras, 2 False Julii Corydoras Salt & Pepper, 1 Bristlenose Plecostomus Hoover, 2 Pictus Catfish, 1 Albino Rainbow Shark, 5 Dension Barbs