Hard to choose one, especially since I haven't found an end-game yet.
Strangely, of all my board I end up using a QFR with MX Reds and custom blank PBT keycaps. The Reds are nowhere near as smooth as I'd like, but the weighting is easy to live with and I prefer linear to notchy tactility.
If I had to choose just one to live with forever, I'd go with the Realforce 87U 45g uniform (mine's a stormtrooper). Smooth, very pleasant sound, subtle, and reliable. Hard to go wrong.