I've had a long standing relationship with
http://www.pr-vacation.com who managed a vacation home for me while I owned it. I thought they were very professional in all my dealings with them.
If your friend chooses to go the rent from an owner route
http://www.vrbo.com is probably the biggest site to use. You'll find a couple of threads asking similar questions on these boards and you can get a lot of the information you require.
The advantage of booking direct with an owner is, generally it's cheaper. The advantage of using a reputable management company is that in the (unlikely)event of something going wrong you are certain to have a local point of reference to deal with that problem. It is a little extra insurance, but obviously that insurance costs a little extra. If you were to book direct from an owner and find that the house wasn't suitable for some reason , the owner might take the view that the objection you have is unreasonable and you should have been aware of that particular issue from the information you were given. They could decide not to repay you (if you moved out) or not help you to find another house. With a management company it is far more likely they will simply switch you to a house where that problem didn't exist (and move another family into the original house, no one loses money, everyone has a house they are happy with). Most owners work pretty hard to work problems through for their guests, but not all do and there can still be occassions where the rentee can have a genuine issue on compatability with a house, but the owner think that's the other persons fault for not asking/explaining it BEFORE they turned up at the house. If an owner has a guest move out of a house at the last minute it's unlikely they will get a replacement booking, as such they are going to be a little slower to accept/suggest the guest moving to another house, it costs them A LOT of lost revenue.
As far as location goes, IMHO the best location if you want to be close to WDW is the area of the 192 that is around the now closed down Splendid China. This is west of the Disney exits from the 192 going towards I27. I think it's mile markers 3 to 6. Developments in this area include ( but is not limitted to) Formosa Gardens, Indian Ridge, Indian Ridge Oaks, Lindfiends and Indian Creek. There is a back route into Disney from this location and all parks are less than 20 minutes by car
in regular traffic. Lots of owners of more remote houses will give commute times of "less than 30 minutes to Disney" but they don't tell you thats either just to get onto Disney property (add another 15 minutes to get to the parks) nor do they say that yes that drive time is possible, if you try it at 3.00 AM with no traffic and break the speed limit. For some people the extra 20 minutes drive isn't a deal breaker, because they go to the parks early, stay there all day, eat at the park or on the way home and aren't too bothered about an extra 40 minutes drive time. If your group is one that likes to take a break in the middle of the day that extra drive time starts to kick in a little, if you also like to go back and freshen up before going out to dinner then you could be taking about spending 5 hours A DAY driving back and forth. That does then become an issue.
