First off, below are the stage measurements taken directly from game data. The second link is the SSBU calculator which includes the rest of the stages the first link doesn't mention.
http://www.kuroganehammer.com/Ultimate/Stages
https://rubendal.github.io/SSBU-Calculator/kocalc.html
Marth in this game compared to Smash 4, with a nerfed Uthrow and a less useful Usmash, favors taking stocks horizontally. Also, as always, Marth struggles against zoning (projectiles).
– So you don't mind a stage with a high ceiling because it probably doesn't affect you as much as it affects your opponent.
– Small stages are also favorable so that Marth can deal with projectiles more easily, allowing more opportunities to pressure his opponent.
– Due to Marth's disjoint (sword), he works well with platforms.
– But he also does well on flat stages against characters that he can juggle effectively.
Therefore...
Marth likes all the stages. It really depends on your opponent.
I have tested this in tournament. It truly is mainly a matchup-based decision with Marth, This is a blessing and it wasn't the case in Smash 4.
