Just to be contrary, I've had good experiences with neons. It seems to me that if you get them past a two-week "break in"/quarantine period, you'll do well. Obviously, others have had different experiences.
Regarding Rummynoses, they're very active swimmers and (just my opinion) do better in a tank longer than a 20-long.
2x20-longs, one heavily planted. Platy rancher. They. Won't. Stop. Breeding.