Re: use pronounceable if you want to remember the password; random otherwise
But then you hit the same problem you do with random letters: if they're truly random, then you're trying to play a word-association game with say "which" and "when" or other pairings for which a mental association is difficult to formulate. And that's just one site for someone with a decent memory (which is why I always retort with "donkeyenginepaperclipwrong" for people with BAD memories such that the word associations themselves become distorted). Now start adding more and more sites to this anagram stew and it's easy to see how you can mix up one mnemonic for another until it's all alphabet soup in your head. I have to put up with people with bad memories on a regular basis, yet they're still expected to go online on a regular basis to do basic management of their affairs.