Really depends on the person.
To me, Baroque is very hard to play. Classical is second. Romantic and 20th century are about equal for me.
I remember the first time I ever played a 20th century piece my teacher said I was really good at 20th century music. This must be true, because I've been playing so much lately... u.u
People like how I play romantic music.
As for Baroque... I'm just not good at it u.u But I'm sure to some people baroque is the easiest.