Hi guys. I would like to know how you all rank these modern concertos (easy-->hard) based on both technical and musical difficulty:
Kabalevsky is by far the easiest of these. It was written as, and frequently taught as, a student concerto.
Ligeti is likely the most difficult of those as it’s really mostly extended technique
I am saying all of this as second-hand hearsay, but I believe Schoenberg is probably in the top 1 or 2 on your list and considered one of the most obnoxious concertos to get your hands around, plus you have to make sense of his weird composer tonal style.
HH's performance of the Higdon concerto is on Youtube. I have heard it but I don't recall it that well - so probably contains nothing too extravagent (unlike the Schonberg, which HH explained in an interview required her to extend her technique to cope with its demands). I have not seen (or looked for) the part.