First of all, chances are you will love wherever you stay! We've been perfectly happy with each level, going in with reasonable expectations. It's all a matter of what you are looking for.
Values have fairly small rooms, the basics, but kind of a busy charm of their own with good food courts. Great for kids especially. Think Holiday Inn equiv.
Mods give you a little more space, a double sink, usually a fancier restaurant and a more themed pool. Nice for families with older kids perhaps? Think Hilton.
Deluxes have a dress restaurant, people fawning over you, all the trimmings. Maybe idea for adults, people celebrating special times. Think Waldorf-Astoria.
Personally, I always start with the moderates, then check the next level up - sometimes a moderate room is only a few dollars more than a value, and in that case I'd take the mod. (Preferably Coronado for us, as you get a health club and the crazy-good Pepper Market which the others don't offer). If not, I'd gladly take Pop or music, and use the money saved for a few special experiences, a special meal or a few quality souvenirs.
No need to fret your decisions though, all the hotels are very nice, all well staffed, all have the transportation and room key charging and so on... you'll have a great trip regardless.