According to fedidb.org/software/lemmy, the top 5 (where top 5 is defined by user count) are:

• lemmy.world
• lemm.ee
• sh.itjust.works
• hexbear
• lemmy.dbzer0

After there’s:

• beehaw
• lemmygrad
• programming.dev
• lemmy.ca

Lemmy.world is pretty safe and generic, but it’s already huge (173k users vs 33k of lemm.ee). Lemm.ee is also a safe bet. Hexbear is totally out of question dbzer0 is great, but it leans heavily in a political direction