@swagmaster You really can't accurately compare Liszt and Chopin, they were so different in style that it's damn near impossible.
That said, if I had to pick one, it would probably be Chopin.
About your qualms with slow sections, it actually dates back to the sonata movement structure- Allegro, Adagio, and the final movement can be just about anything, though often it's a rondo.
As far as romantic music is concerned, keep in mind improvisation was a huge source of material for many composers. Slower sections also give nice contrast to constant speed and power- it makes the faster sections just that much more powerful.
I thought much like you at one point (hate to say this, it's corny as hell and slightly condescending), but I came to love these slow sections; when things are simply fast all the time, it gets boring. I can only listen to Chopin's Revolutionary Etude so many times before it gets boring.
Also, Chopin doesn't always go slow

Examples of that are basically all the etudes. And some miscellaneous works.