With schoolers I think rummynoses are indeed at the top. But with harlequins i think they loosen up over time.
With cardinals I've found that they school better when they're the only fish in the tank (apart from the few clean up crew members). They school a lot better now after I took the SAE's and roselines out of the tank.
Espei's are good. Especially since they're smaller. They're several choices out there. You just need to choose which you prefer and contrast in color and such.