This is an interesting topic. It seems to me that if we're going to factor in price, we also should take the age of the kit into consideration. Depending on whether we do or don't do that, I think I can make an argument for putting the same kit close to the top of both the "Best" and "Worst" lists.
The old Revell 1/535-scale U.S.S. Missouri was originally released in 1953. It was Revell's first ship kit, and one of the very first plastic warships from any firm. Varney and Lindberg have some claim on the title "First," but the Revell Missouri certainly was a major figure in the first generation of plastic kits. It featured a level of detail that kit purchasers had never seen before. (Compare it to the balsa version from Monogram, for instance.) It captured the imagination of tens of thousands - probably hundreds of thousands - of kids and adult modelers. It surely was a huge factor in creating the hobby of plastic ship modeling. If we evaluate "quality" in terms of importance and influence, this kit may well belong among the "top ten." Certainly the "top hundred."
But by the standards of 2009 the kit is, regardless of what new-fangled box it's packed in, a real dog. Its hull is inaccurately shaped (largely because the hull lines of the Iowa class were still classified in 1953). It has no screws, and it's missing a rudder. The Oerlikon guns are represented by three-pronged blobs cast integrally with the deck. The guardrails look like slabs, several feet thick. The barrels of the Bofors guns are flat on their bottoms. By modern standards the thing looks more like a toy than a scale model - and it could well be argued that it's one of the worst ship kits ever.
Matters of deep philosophy aside, I'll take the liberty of disagreeing somewhat with my cyber-friend JMart and suggest several sailing ship kits that I think belong among, or close to, the "top ten":
Heller 1/100 H.M.S. Victory
Heller 1/75 La Reale
Revell 1/96 Constitution
Imai 1/120 Cutty Sark (and probably several other Imai kits; I haven't seen all of them)
Revell 1/64 Viking ship
Revell Mayflower (either scale)
Revell 1/96 Golden Hind
Revell 1/110 Charles W. Morgan
Airfix 1/144 Wasa
Sheesh - that's nine. I wouldn't want to argue that nine out of the top ten ought to be sailing ships; comparing sailing ship kits with modern steel ship kits really is like comparing apples and oranges. But those nine, despite the fact that all of them are at least thirty years old, can, in my opinion, hold their own against anything the industry has produced since.
As for the "bottom ten" - taking into due consideration the date factor I mentioned earlier, I nominate the Aurora U.S.S. Halford. It was labeled a Fletcher-class destroyer (which the real Halford was) equipped with an aircraft catapult (which the real Halford was). And the picture on the box showed a catapult-equipped Fletcher-class destroyer. But inside the box was an extremely crude model of either a Sumner- or Gearing-class ship. (It was so crude that it would be hard to tell which.) It had a catapult, all right - which none of the Sumners or Gearings did. And the aircraft on the catapult bore no resemblance to - well, much of anything. Even by mid-fifties standards, that was a lousy model.
And then, of course, there's the Revell "H.M.S. Beagle," one of the more egregious marketing scams in the history of the hobby business. And the same company's "S.M.S. Seeadler" and clipper ship "Staghound" - more of the same. The grossly misproportioned Heller "Oseberg Ship" surely belongs on that list. Come to think of it, I'd include quite a few of those old Heller kits that used identical hulls dressed up with decorations that turned them into travesties unlike anything that ever floated.
That "bottom ten" list is a pretty depressing subject. Better go to bed.