JJ 6V6S's are cool. They sound a bit more open than standard 6V6 types. They have more headroom, lows, and highs (more 6L6-like) than average 6V6's.
Tung Sol 6V6's are cool if you want a more traditional 6V6 sound. Smoother, creamier, and more compressed than the JJ.
Ruby Chinese 6V6's are more traditional 6V6-like than JJ's, but not quite as smooth and creamy as Tung Sols. They seem to have a slightly grainy/grindy high-mid voicing to them.
Tung Sol 5881's are great, but not all amps can use them. Most of the time, they are not a direct substitute for 6L6's because they can take less plate voltage than 6L6's. If your amp can run them, they're sort of an in-between 6L6 and 6V6 type. They have less bass and headroom than standard 6L6's, but are more open and chimey than 6V6's.
I know they usually get a bad rep, but the cheapie Sovtek 5881/6L6WGC's have proven solid and reliable for me. They have this sorta grindy high-mid voicing that cuts through great in a mix. JMO, of course.
If you want smoother, the Tung Sol 6L6GC-STR's are killer too. Less scooped low-mids than the Sovtek and smoother, creamier up top. Tung Sol power tubes in general seem to be voiced that way, IMO.
