You are quite right, Babek, two-syllable adjectives ending in -y have -ier and -iest as their comparative and superlative. Thus:

• Yours is the messiest room I have ever seen.
• She was the prettiest and happiest girl at the party.

Note that other common two-syllable adjectives ending in an unstressed vowel normally take the -er/-est patterns:

• The cleverest solution to any problem is usually the simplest one.

Others, particularly participial adjectives formed with -ing and -ed and those ending in -ious and -ful form their comparatives and superlatives with more and most:

• Watching cricket is even more boring than playing it.
• My wife was certainly more anxious than I was when
  Penny failed to return.
• I bought the wrong type of hair shampoo for Joan. Next
  time I was more careful.

Note that most sometimes means very:

• I was mostcareful to leave the room as tidy as I had
  found it.
• I became mostanxious when I heard that there had been
  a fire at the hospital.
• I was most impressed by Deborah’s performance as Lady Macbeth.

With some two-syllable adjectives, er/est and more/most are both possible:

• The commonest /most common alcoholic drink in Poland is vodka.
• He is more pleasant /pleasanter to talk to when he has
  not been drinking.

Three or more syllable adjectives take more or most in the comparative and superlative except for two-syllable adjectives ending in -y and prefixed with un-:

• John is the unhealthiest person I know, but one of the most successful.

Hyphenated adjectives, which are also known as compound adjectives, normally use more and most for the comparative and superlative forms. This is the general rule. Sometimes we have to use more/most if, for example, the adjectival part of the compound ends in -ed. So, sun-tanned would have to be more sun-tanned, just as tanned would have to be more tanned:

• You’re more sun-tanned than I am.

Sometimes it is not so clear-cut, so we would say that one form is more likely than the other. In your examples, Babek, both are quite possible, it seems to me.

If you want to try some examples look at our Message Board in the You, Meand Us part of our website.