I made a Spreadsheet where I gave a rating for all players in the 2012-14 classes on a scale from 1-4. By now we have at least an idea how good these players are/will be, not based on rankings, but based on how they have looked on the field, and how much they have played. I then compared them to the recruiting rankings from various services to see which ones were the most accurate:

ESPN
Rated 3 stars (in the 70s): actual 3.18
Rated, but rated in the 60s: actual 2.5
Not rated (40-45 rating): actual 3.09

Scout.com
Rated 3 stars: actual 2.86
Rated 2 stars: actual 3.12

Rivals
Rated 5.5 or up: actual 2.71
Rated 5.4: actual 2.84
Rated 5.3: actual 3.00
Rated 5.2: actual 3.10

247Sports -Their rating, not composite
Rated 80+: actual 2.92
Rated 75-79: actual 3.11
Rated 71-74: actual 3.00
Unrated/rated 70: actual 3.33

247 Composite:
Rated 80+: actual 2.78
Rated 75-79: actual 3.09
Rated 71-74: actual 3.22
Unrated/rated 70: actual 3.25

The clear winner here was ESPN. Those they ranked highly did fairly well, while those they ranked poorly did poorly. Unfortunately they only rank a handful of players who go to Ohio, so the results aren't statistically significant.

In second place is 247Sports. Their results are uncorrelated, with no significant difference in performance between highly ranked and low ranked players.

In last place comes Rivals and Scout, which both have striking inverse relationships. They higher they ranked a player, the less likely that player was do well. Since the 247Composite included their rankings, that ranking also has a striking inverse correlation.

This doesn't mean that highly rated players are always bad, nor that low rated players are always great, just that the low rated players have tended to be a bit better, on average. To illustrate the differences, here are are two lists. The first is the players who had 247Composite 3-star ratings, and the second is the unrated players. There are good players in both groups, but the very best players are in the unrated group, and there are less players who never were starters in the unrated group:
Sebastian Smith .85
Joey Duckworth .84
Jared McCray .84
Joe Lowery .82
Robbie Walker .81
Zach Murdock .81
John Tanner .81
Justin Wyatt .80
Greg Windham .80
Corey Quallen .80

Unrated players:
Tarrell Basham .70
Blair Brown .70
Davon Henry .70
Toran Davis .70
Maleek Irons .70
Brendon Cope .70
Kylan Nelson .70