In general, I'm more likely to feel contentment than joy, which is part of the nature of both of those feelings. Day-to-day, contentment is like having a pitcher of water, full, and sometimes, perhaps, spilling over, but mostly still and quiet.
Joy, on the other hand, is the shaft of bright sunlight that bursts out from between thick clouds in a summer thunderstorm, and more often than not, it catches me by surprise, brings tears to my eyes, snags my breath in my throat. Every one of these moments, whether fleeting or holding still long enough for me to trace its outline into my memory, is like a gift from chance to me. It may be sitting around the dinner table with heart-friends, playing Scrabble with a kid with a secret weapon, seeing a baby of my acquaintance laugh, or fall asleep in my arms.
Sometimes, I can put myself in the way of joy, most reliably by dancing, which it's easy for me to put off doing, but every time I do, I'm reminded that I shouldn't.