Why people says SE is better PP

 I like sausage pizza

SE no cross over distortion, low power. PP cross over distortion much more power. now how about SEP single ended parallel. no cross over distortion more power mmm

There are some theoretical problems with parallel SET topology.  Some designers claim that it is hard to avoid one tube in a pair from becoming a "current hog" and seemingly end up doing most of the work while the other tube puts out much less output.  There is also the claim that having multiple tube tends to make the sound less pure and a bit more "muddled" because the sound of the tubes is never perfectly matched (this would be an argument against ANY design with multiple devices providing the output).

I own a parallel SET amp (Audio Note Kageki).  I like the sound so I cannot say whether these theoretical problems actually do affect performance.  But, I will note that the output tubes do tend to become unbalanced over time, with one testing much stronger than the other in the pair for each channel.

The advantages of parallel output tubes in a SET are not only higher output.  Using parallel tubes will also lower output impedance which means that damping factor will be increased or the designer can reduce the turn ratio between the primary and secondary windings of the output transformer.  

I am guessing that there must be some challenges to making good parallel SET amps; my guess is based on the dearth of such designs on the market.  

I would also dispute the notion that any particular design is inherently better than another.  I've heard very fine examples of pushpull, SET and output transformerless amps (OTL).  The amp I currently favor in my system is a pushpull amp (I still do like the Kageki, which I have loaned to a friend).  One of my all time favorite amp is an OTL amp.

I built OTL 6AS7 GE & ECC81 and it is my favorit. In OT amps sound and the bass are defined by quality of OT. How sound the amp deppends how sound the OT /the best OT is missing/.About PP and SE. Crossing of the signal 0 between upper and down sholders of PP cause sharp and metal sound, that people define like detail sound. 

No matter the topology of an amplifier each will have it’s advocates and invariably detractors, no exceptions. SET has been the most satisfying choice for me, yet certainty OTL or class A solid state for others. There’s variation and a hierarchy within each specific topology. I could never proclaim or bestow "best " for any of them. You listen and eventually you’ll find what suits personal preference and objectives. So many variables, all SETs don’t sound the same. Listen to for example OTLs, Atma-sphere, Einstein Audio,  Joule, Tenor each has it’s own sonic signature. This is true for any and all amplifier genres/topologies.
Charles