Well they all are rated to stand high plate voltage. Standard EL34 specification is 800vdc, far far above the plate voltage provided by any guitar amp you're likely to find. Screen voltage tolerances, however, are quite low, from 500v to sometimes as low as 425v depending on the particular tube make and model. Excessive screen voltage will destroy an EL34 in fairly short order, as the EL34 by design is screen-current hungry.
Microphonic isn't so much a concern with power tubes as it is with preamp tubes, because the power tubes are much less sensitive to noise generated in the power section itself. You might get a tube where you can hear yourself through the speaker by tapping on it, but the squealing and other nastiness typical of microphonic preamp tubes is an artifact of said noise being amplifed several times before hitting the output.
Now, with all that jabber out of the way, I personally really love the TAD EL34BSTR. It's very similar in tone to the Ruby BSTR, but has some seriously rugged internals that are supposedly a step above the Ruby. Now that Winged C's are no longer in production I would bet the TAD's are poised to become the new "It" EL34.
