1. contest of champions 1
2. contest of champions 2
Never read these
3. secret wars 1
IMO one of the best events ever, also the one that really introduced me to comics (the first comic I ever actually read was an Ultimate Fantastic Four comic back in 2005 but Secret Wars I was the first event I really read). It basically had everything you could ask for in an event - some of the most iconic heroes and villains all doing their thing, all getting chances to shine and show off their unique methods and plans, as well as huge battles, a neat backstory, and of course the Doom, Galactus, and Beyonder stuff. There are so many great scenes (Galactus snuffing out Ultron, Molecule Man dropping a mountain range on the heroes and Hulk holding it up, Spidey fighting the X-Men, Human Torch vs. Ultron, Magneto and Professor X trying to read Galactus's mind, the heroes' attack on Galactus, Doom and Klaw vs. Galactus and Beyonder, etc.) Personally this just defines the ideal comic book crossover event for me.
4. secret wars 2
Not nearly as good as the original but a lot better than most people give it credit for. Overall I did like it and would gladly read it again
5. acts of vengeance
Only read parts of it, from what I remember it was okay
6. Infinity Gauntlet
Very good, I'd put it above Secret Wars II but below Secret Wars I
7. Infinity Crusade
Meh, not as good as Infinity Gauntlet or Infinity War, but okay
8. Age of Apocalypse
Never read it
9. Onslaught/Heroes Return
Read parts of it - not all that good
10. Avengers Disassembled
Never read it
11. House of M
Hated it, couldn't get past the first issue
12. Annihilation
Great, the best of Marvel's cosmic events of the entire decade
13. Civil War
Not quite as bad as some people make it out to be, but still not all that good
14. World War Hulk
Many people dislike it, but I thought it was pretty good. Filled with PIS fights, but other than that I liked it
15. Secret Invasion
A little below average
16. Siege
Have to admit I liked it, despite it being anticlimactic
17. Chaos War
It was fun in terms of huge cosmic events, even though a lot of it didn't make all that much sense. I liked Hercules getting the spotlight, though. I'd rank it solidly above average
18. Fear Itself
Again, better than most people say it is. Odin's big mean older brother who we had never heard of before was certainly an asspull, but I like the concept of the many different hammers possessing the characters and turning them into the Worthy, many of their designs were also very cool looking. The Serpent's ultimate defeat was anticlimactic, though (He really should have read the Evil Overlord List, especially point 34)
19. AVX
Like I said before, the only good part of it was Hope punching Cyclops to the moon
20. Infinity
Could have been good, but tried to do too much in too short a time. The Builders plot was such bullshit, they are built up as this incredible, unstoppable threat, but then suddenly the tide turns and they get their asses kicked. Lots of potential there if they didn't screw it up, but they did. The Thanos stuff was better, but the ending to that also came too quickly and was a major DeM
21. Original Sin
Haven't read it
DC EVENTS
1. COIE
Classic. I read it as I was first getting into comics, shortly after reading SW I. I didn't recognize most of the characters, but even so I really enjoyed the story. There's just so much going on but it never loses track of the main plot, and it has so many great moments, like Barry sacrificing himself and the final battle against the Anti-Monitor
2. Millennium
Never read it
3. Armageddon
Never read it
4. Zero Hour
I liked it, for the most part, Extant and Hal as Parallax were cool
5. Underworld Unleashed
Only read like one tie-in, don't remember much of it
6. DC vs Marvel
Meh
7. Genesis
Liked it, I generally enjoy the Fourth World stuff
8. DC One Million
Great event, lots of new and interesting ideas, and it basically introduced an entirely new setting with its own set of characters which was really fascinating, I also like how it spun off into stories like All-Star Superman and various other titles
9. Our World's At War
This is another one I would say is better than most people give it credit for, but not that good either
10. Identity Crisis
Never read it
11. Infinite Crisis
Tries to be what COIE was and fails. Not horrible, merely passable
12. 52
Excellent, has a lot of time to build up the story which it does well, tying all the plot threads together. Basically a model for how to do an event story
13. Amazons Attack
Never read it, and judging by Linkara's review I never intend to
14. Final Crisis
Kind of confusing, although the tie-ins partially explain it, overall better than Infinite Crisis but still no COIE
15. Blackest Night/Brightest Day
Blackest Night was fun, Brightest Day didn't quite measure up
16. Flashpoint
A jumbled mess. I really didn't like it much at all.
17. Trinity War
Never read it
18. Forever Evil
Never read it