Bernhard, I disagree about March of the Trolls being in the Advanced level.
It's a free country!

As with everything else in the universe, it depends.
As I said in my first post, difficulty is always subjective and personal. March of the Trolls (incidentally, there is a mistake in my original post: it is not Op. 32, it is no. 32, Op. 54 no. 3) is advanced when compared with the other Lyric Pieces, not when compared with the general piano repertory. In fact it is around (or slightly above) grade 8. I would guess. Now the ABRSM considers grades 1- 3 beginners grades, grade 4 - 6 intermediate grades and grades 7-8 advanced grades. Yet, grade 8 does not even begin to touch the easiest virtuoso pieces (whatever you want "virtuoso" to mean). Therefore we would probably have to start another fun thread to endlessly discuss the meaning of "advanced".
For a concert pianist like Emil Gilels, or Leif Ove Andnes who recorded several of the lyric pieces, March of the Trolls is probably a "beginner's piece" when compared with their other repertory.
However, the original post stated quite clearly that:
"I'm thinking of using Grieg's lyric pieces for intermediate level piano students, but iIm interested in pianists opinion about the level of difficulty, that is, which are the hardest, easiest etc and which have most teaching value. the brooklet seems like it would be relatively difficult for beginners whereas the waltz in the beginning seems rather easy but I'm not certain for what grade students it would be suitable. "
Since my main aim was to provide some helpful input to Sel, and since I took "intermediate pianists" to mean someone who is around grade 4 - 5 ABRSM, I believe that classifying March of the Trolls as advanced was both helpful and accurate.
To such a student, the Waltz Op. 12 no.2 would be about right, Brooklet Op. 62 no. 4 would require a lot of work for an intermediate student and be just about impossible for a beginner, and March of the Trolls would definitely be advanced.
However, if you are already playing Slamey, Scarbo and the Prokofiev Toccata, then it's a different matter altogether.
Best wishes,
Bernhard.