We've stayed at all three. A little about "us" (my wife and I). We spend most of our time in the parks, we enjoy using the pools to cool down. We do not travel with children. We ALWAYS rent a car (no buses for me, so transportation is usually a non-issue - i say usually because sometimes I prefer not to drive home after a day in Epcot if you catch my meaning). We are double income no kids so budget is normally not a major concern.
What we've found:
Pros to Deluxe: It was nice to walk to Epcot and take a boat to HS.
Negatives: Same quality rooms as moderate, same quality of food service, pools are no wetter than anywhere else.
Moderate Pros: Theming is as nice as the Deluxe (in my opinion), love POR. Very nicely themed and enjoyable pools. Rooms are nice.
Moderate Cons: A bit pricey if all you're doing is hanging at the Parks.
Value Pros: You're on resort, so you get the benefits that come with it. The rooms are clean and reasonably priced.
Value Cons: Crowded, can be loud.
For us we are generally willing to spend the extra money for a moderate. We find a big difference in quality and theming between them and the values. The deluxe resorts just don't warrant the significant increase in cost. My opinion, if you can afford it, get to a Moderate resort for better theming, restaurants, pools and slightly larger rooms. Skip the deluxe unless you really put a lot of value on riding a monorail, boat or walking to a park over renting a car.
BTW - a weekly car rental is usually about $175/week for an economy car. Much less expensive than paying $1000+ for an upgrade to a Deluxe, and parking on resort and at parks is free with any hotel on resort.