congos are aggressive.. and cardinals (similar to neons i believe) don't really school that well. my neons are bottom dwellers. they stick together, but don't school that well.
i've heard rummy nose school the best. i have a school of about 20 or so harlequin rasboras. they school extremely well and are in the upper water column. works great for my tank because my neons are bottom dwellers and my harlequins are upper water column dwellers. it's rare to see the two schools cross.