In my point of view, the Preludes are a good start because they are short.
No. 4 in E Minor was the first that I did. It's a neat piece, and Chopin in fact requested it to be performed at his funeral. You could look at the list of the preludes on this website; it has a grade level for each one. You also might want to check out some technical exercises just to rebuild your muscles. What were you playing before your hiatus? That might help to decide what you should do next.