I think the definitions of the words have kind of changed through the years.

To me, both "hunk" and "stud" can be used when you are just talking about a hot guy.

"Hunky" does seem to be used more when talking about guys with muscles.

"Stud," however, can be used to talk about anyone who you think is sexy.

"Twink" is traditionally meant to refer to a young, kind of feminine acting boy with "twinkle"-esque features.