The serialized stuff is really important and weaves through most, if not all, episodes of the show (there are multiple antagonists and plotlines). But if you're looking for just the best one-offs, here's what I'll recommend:
Season 1, Episode 4: Cura Te Ipsum
Season 1, Episode 8: Foe
Season 1, Episode 21: Many Happy Returns - This is one of those "personal backstory" episodes, it's not really related to the overarching storyline, but it does give you the backstory on one of the main characters. Good episode.
Season 2, Episode 14: One Percent
Season 2, Episode 17: Proteus
There are lots more great episodes in Season 2, but they've begun arcing storylines (so, like 4 episodes are part of one long storyline), so if you don't want serialized stuff, I can't put it on the list. But man, trust me. This is a fantastic show. There haven't been any bad episodes at all. The serialized and overarching plotlines are really engaging, easy to follow, but super interesting. Deals with a lot of interesting themes like AI and surveillance.
If you can, watch in order from the beginning. But the ones I listed above you can probably watch at any point so it won't confuse you.