For example, the word 'socks' is lovely to say. It kind of slips off the tongue in a whisper of breath. It's a happy word, and one of my all time favorites. 'Spongy' on the other hand, is one of my least favorite words to say. It's harsh and just feels icky. I don't know why...
Another word I love is 'morbific'. This one is just fun to say. I also love its meaning: so filthy as to be death inducing (I'm paraphrasing there). I also like 'preposterous' which is a criminally underused word for something so delicious to enunciate. 'Wither' is another great word, one that actually sounds like its meaning.
All kinds of words that describe actions with specific sounds are great: 'crinkle', 'crumple', 'smash', 'shatter' - all fantastic verbs that sound like the noise they make. A lot of verbs are like this, very much like the action they portray. 'Sprint' for instance is a short dash of a word, while 'meander' kind of ambles all over the place. 'Tumble' bounces and drops from the tongue, while 'soar' just flies up off it.
What words do you love? Which do you loathe? Why?