This has been an issue brought up more often recently now that 247 Sports seems to be making a strong push in the recruiting world. I have to admit that I used to be strongly entrenched in Rivals' camp, at least as far as Michigan-related sites go. Lately, I have been looking to 247 Sports more and more. Underneath the votes I have some pros and cons for each sites:
Rivals has shown to be the best when it comes to recruiting rankings. The guys who go on to NFL careers were generally rated higher by Rivals than ESPN or Scout (247 Sports is too new for this to be relevant). The site is also easily navigable, and it's simple to sort through positions, recruiting classes, schools, cities, etc. The Wolverine, which is the Michigan-specific site, lost a lot when Josh Helmholdt got promoted to midwest analyst. His replacement, Tim Sullivan, doesn't have the contacts or the football acumen to fill Helmholdt's shoes, so content on The Fort (the premium message board) has been lacking and/or slow.
247 Sports: 30%
247 Sports popped onto the scene with some technological advancements that sped past its competitors. If you go to a recruit's profile, it has a timeline that reports dates of offers, camp visits, campus visits, official visits, commitments, etc. It also links highlights from various other sites (Youtube, Hudl, etc.) and shows a Twitter feed with mentions about that particular player. The two newest features are the 247 Composite ranking (which averages together a recruit's rankings from the four major sites) and the Crystal Ball, which shows updated predictions on where the prospect will go. The message board can be a little unwieldy, but writer/moderator Steve Lorenz does a good job of keeping up with recruits, even some that are just barely on the fringe of Michigan's radar.
Scout seems to have been most affected by the arrival of 247 Sports. The website is very difficult to navigate and looks like it was designed by amateurs. (By the way, I freely admit that I'm an amateur when it comes to site design, so I'm not handing out criticism I'm unwilling to take - but this is a hobby for me, and it shouldn't be for them.) The best thing Scout's Michigan site has going for it is Sam Webb, who seems to be the guy most plugged in to Michigan's coaching staff and the program. Finding rankings by position, state, etc. can be difficult with Scout, so I mostly avoid the site, except when a) a player commits and I need his Scout ranking or b) they update their top 300.
None of the above: 11%
These people probably either don't care about recruiting or they just care about the free stuff that filters over to free sites, message boards, etc. To each his own.
As far as recruiting goes, Wolverine Nation's Tom VanHaaren does a great job of keeping up with recruiting news. He and 247's Lorenz both seem to be on a fairly even plane. The message board gets updated regularly, and the moderators spend plenty of time online. Chantel Jennings adds some feature-like items and Michael Rothstein handles mostly basketball recruiting stuff and then some features on current and former Michigan players, so it's pretty much VanHaaren's show. ESPN is slower to rate players and updates its rankings less often; whether that's good or bad might be up to its audience to decide. Personally, I think rankings are updated too often by some other sites (especially 247), but ESPN could probably start earlier with their initial rankings. Individual recruiting profiles lack highlights or links to highlights, so the site relies solely on ESPN videos of camps and such, which load slowly and are full of commercials. I would expect a better product for all the money ESPN has to throw around.
Full disclosure: I currently have Rivals and 247 Sports subscriptions. I let my ESPN subscription expire. I have never been a member of Scout.