What I think are the 12 best Silver Age issues:
12. X-Men #64 - "The Coming of Sunfire!"
11. X-Men #60 - "In the Shadow of...Sauron!"
10. X-Men #57 - "The Sentinels Live!"
9. X-Men #61 - "Monsters Also Weep"
8. X-Men #62 - "Strangers in a Savage Land"
7. X-Men #13 - "Where Walks the Juggernaut!"
6. X-Men #14 - "Among Us Stalk... the Sentinels"
5. X-Men #4 - "The Brotherhood of Evil Mutants!"
4. X-Men #1 - "X-Men"
3. X-Men #12 - "The Origin of Professor X!"
2. X-Men #59 - "Do or Die, Baby!"
1. X-Men #58 - "Mission: Murder!"
I recommend that anyone who's having a really tough time consider using the CMRO, as it lists issues that are deemed essential while others can be skipped over without losing too much understanding of what's going on.
https://cmro.travis-starnes.com/titl...0&title_id=214