It's an interesting exercise and as Ricco says, quite subjective. I compiled my own list as per the below to see how my own ratings would go and came up with something different. It's a tough comparison with different view points rating things differently.
These players are also just reaching their peak at this point in their career so there's still plenty of room for others to join the elite categories. Player development and opportunities do differ from club to club which has a huge impact on how each player fares at AFL level so top talent can be squandered by clubs. Then there's things like injuries and roles within sides that can effect players impact and development.
In any case, I've composed a list of what I would consider great players from each of those drafts for comparison. Each draft is not the same as others with different talents available. For example this year is supposed to be pretty even from 3-30 with it being hard to split a lot of those players making second round picks very valuable. Last year, the top 7 was considered as good as any year ever with a big drop off after that. It all just depends on the kids available.
2011 Draft Notes - 26yo at present, this draft was heavily compromised by GWS who had 11 of the top 14 picks and O'Meara and B Crouch going in the mini draft this year who would have otherwise been eligible:
2. Coniglio, 6. Wingard, 11. Greene, 12. Doherty, 13. Adams, 14. Smith, 21. Mitchell, 25. Ross, 30. Yeo, 32. Hamling, 33. Hill, 58. Neale, 67. Witts
Total - 13 great players
2012 Draft Notes - 25yo at present, this draft was considered strong at the top end and tailed off. The only players considered great after the first round were father son selections. Hogan and Martin went in the mini draft similar to O'Meara and Crouch:
1. Whitfield, 5. Stringer, 6. Macrae, 7. Wines, 9. Daniher, 18. Grundy, 26. Viney, 49. Hunter
Total - 8 great players
2013 Draft Notes - 24yo at present, this draft year ran deep and had an even spread of talent:
2. Kelly, 3. Billings, 4. Bontempelli, 11. Sheed, 13. Cripps, 23. M Crouch, 26 Merrett, 29. Lobb, 35. Nankervis, 37. A Pearce, 44. Aliir Aliir, 47. Brown, 55. Fantasia, 56. Sicily
Total - 14 great players
2014 Draft Notes - 23yo at present, this draft is harder to judge with players only just reaching their best years now and there being plenty of time for players (especially KPP) to step up:
3. Brayshaw, 5. DeGoey, 9. Moore, 13. Weller, 14. Lever, 18. Heeney, 24. Steele, 26. McLean, 29. Miller, 46. Daniel, 54. Langdon
Total - 11 great players