I’m not a linear switch guy, so don’t take my opinion as gospel, but I don’t like either MX red or MX black. One isn’t stiff enough, and the other is too stiff. I personally think the reasonable range of stiffnesses for linear MX switches is from “62g” to “67g” “Korean” springs, or the springs from MX clear switches are also kind of interesting. Linear MX switches really need some lubricant added to be pleasant; unmodified, they’re quite frictiony.
Alternately, black Gateron switches from
https://geekhack.org/index.php?topic=68943.0 should be a pretty good weight, and a bit smoother than current MX switches.
Better still, both white Hi-Tek “space invader” switches, and green complicated Alps are quite nice linear switches, if you can find them in good condition, though obviously neither is compatible with keyboards designed for MX switches.