I like vacuum. That way particulates in the solution are removed. If you dry, they are deposited in the groove. I use a basic Nitty Gritty that I already had.
Yes, removing the liquid+particulates in solution with a vacuum RCM is absolutely necessary ... unless you have added a pump & 1 micron filter setup to your US tank!
The filter removes the crap in solution - so it no longer is deposited in the grooves. Which means you have to only get them dry, somehow.
Some people air-dry them in a dishwashing rack; I think this allows dust to settle on them - so I use the Dryer Cube from ultrasonicrecords.com for this (with a filter on the fan's air input hole).