What are the premium domain letters and what are the bad domain letters

People ask this question quite a bit so I thought I would post what are considered premium letters, mid range letters and bad quality letters when it comes to domains. Now, for many domains it may not make a difference because a good domain can have what is considered bad letters. here are the different levels of letters in domains:

Premium: A, B, C, D, E, F, G, H, I, L, M, N, O, P, R, S, T

Mid level: J, K, U, V, W

Low level: Q, X, Y, Z

These levels are made because of most common useage in the english language mostly. So when determining value of domains such as three letter and four letter domain names, these levels come into play. However, that doesn't mean that there aren't good domains that have "bad" letters. An obvious example is sex.com which has 33% of the letters in the domain considered bad. Sex.com sold for millions a few years ago.

OK, that is a pretty obvious example, but I think you get the idea.