JJ's and Svetlana's are the best *currently being made*.
Telefunken made great 12AX7's, but I don't know about their power tubes.
Sovteks are alright, but the 5881 isn't as loud as a regular 6L6 and they seem to wear out rather quickly. Their pre amp tubes tend to go microphonic as well.
Phillips are good, but I don't think they're being made anymore, and they go for twice the price of Svet's or JJ's.
Mesa just uses junk Chinese tubes. Groove Tubes uses tubes from all different brands, they just test em, match em, and slap their name on them and double the price. "Fender" tubes were Sovteks from 95-00, now they're Groove Tubes.
Bottom line: Get something from your local amp shop or NOS tube shop. They'll probly test burn em and they are about 579108754 times more knowledgeable than someone at Mars or GC.
Sylvania, GE, RCA, and Mullard are also good, but they're only available NOS, and probly a higher price than JJ or Svetlana.
Check out alt.guitar.amps for more info.
I would also like to request that one of these tube threads be put in the FAQ section. These tube threads seem to pop up rather frequently.