Count me among those who prefer a good EL34, such as the JJ, over the 6550, KT88, and KT90. The midrange, which gives "life" to the music is simply light years better. That being said, I have seen more than a few amplifiers that for whatever reasons (maybe improper bias?) that can run both, and just do not come alive with an EL34.
Another option is the JJ KT77, or the 6CA7 which is offered by Ei and ElectroHarmonix. My experience with the KT77 was that it was a good compromise between the JJ E34L and their KT88 - powerful lows of the bigger tube, with superior mids (though still not close to the E34L).
I've been meaning to write up the tube shootout our audio group did in three separate systems - 1960s Mullard XF1 EL34, JJ E34L, EH EL34, JJ KT77, JJ KT88, but have never gotten around to it. For what it's worth, the conclusions were pretty consistent...