El34 = KT88 = KT120

Sure the KT120 is 2x;'s the size of a EL34.
But in my limited expereince ((thus far,,have 1 more experiement just ahead when my new speakers arrive and I build the cabinet, then further testing of the 3 types can begin) 
You get something nice of one tube vs the other 2, and another of he 3 shines better here, the last is slightly superior in this/that aspect.
6 of 1 /half dozen of the other.
I mean it all boils down  gain here, and give up something there.

Power  tube = power tube. 
I would not make such a  big deal over the comparisons. 
Thats said.
I think for me , i prefer the EL34 of all power tubes (as I've been told its the best of the 3) , Why?
Because its the ideal tube in a  PP amp for a  single wide band speaker. 
But i could be wrong, 
Will test out the 3 tubes in a few weeks. 
I actually could not hear much differences on the Seas speakers. All 3 sounded so very close. 
You might say the Kt120's out shoot the tiny EL34 in the  low bass fq's. 
I have Mundorf caps in the amp, these high end caps  adds a  nice punchy bass to any tube in the socket. 
The EL34 has just about same bass as the huge KT120's. 
I just don't see much difference  to debate the issue.