I think that my favorite sounding board is either my QFR with MX Reds, or my BlackWidow (2012) with MX Blues.
Although it has to be said that my BW sounds a little crunchy compared with QFR and Filco with MX Blues, from what I've seen on YouTube... Like I'm hearing and feeling play in the keycaps, making them a little more squishy and rattly. They seem to sound more clean and crisp, which is what I'm really after. My QFR certainly feels more solid, so I might try to get one of those with MX Blue to replace the BW.
I tend to prefer the sound of all my keyboards (except the Model M) when they are on a soft pad or on my lap.
I'm thinking of getting some rubber bands for the spacebar to make it sound less distinct from the rest of the keys.
This is the sound I'm after, more or less: