RE: I'm choosing a cover, not a college...
I would personally get the Nikky's. I have tried all three of these types of covers, and the Nikkys were my favorite. They remind me of a great fiiting trim disposable diaper. They are high cut enough in the thigh area that they don't cover the top part of your baby's thigh, making it difficult to move around, and leaving red marks--as the Bumpy covers did on my DS Joshua. But, Nikky's are still cut generously enough that you can trifold a prefold and lay in into the cover, and it still fits (this dosn't work with some other trim covers.)
The Bumpy covers were wider all over, and covered up too much stomach area and leg area for my cruising baby. I loved the soft knit outer print cover, but I can see that after many washes it will be all faded looking. Too bad, beacuse I wanted printed diapers. but this way, there won't be anything to fade, and the solid white will be good for a boy or girl with my next child someday.
The Nijis were really more for skinny babies with thin thighs. I wouldn't bother if Gracie has average to chubby thighs (as most babies do).
Happy to help,
Mama to "The Fantastic Four":
DS 02
DD 06
DS 09
DD 12