Of course it all depends on your amp's circuitry... brighter tube for a darker amp, and vice versa...
That being said, I have a thick-as-a-milkshake JTM45 mutt (I customized), and I use EH 6CA7s... spank 'n' clank and a deep bottom.
Tried Tung-Sols, but they had no sparkle. Very middy - prolly good for modern amps that are super-thin sounding.
EXTRA: For KT66s, Valve Arts used to be good; haven't used them in a long time though, so can't say.