Triode or Ultra-linear? Why?

For R&R, UL  seems to be the preferred mode, since you want a little extra umph for the drum/bass. Typically any instrumental-R&R,Jazz, Classical I leave my PL in UL.

Jazz vocal divas-Ella,Billie, Sarah..etc I prefer triode, which "pushes" the band further behind the vocalist.

If I had to choose only one, I probably would choose triode.

lloydc-I heard the Mesa years ago, isn't there an option to run full pentode as well? 

From what I remember, the Mesa is a fine piece, just like their guitar amps.

I find my lofi tubed system absolutely needs the UL/triode option. The majority of my listening is records, many are simply too "hot" when cranked 
ocaissionally in UL. Hearing a Les Paul or cymbals at near concert levels isn't the same when I heard the same song 40 years ago.

UL for me is also a "loudness" switch when listening at low volumes.

I suppose  actual system configuration also,determines what you like.

Presently listening to SD "Katy Lied" in triode. Sounds pretty good for an album they hated for its SQ.