I also lean toward giving medals to players who have less of them (often newer players, but not always). I might implicitly trust an established player that I've interacted with regularly, but if they already have 15 trust medals, my usual thought is "What do they need another one for? It's already obvious to anyone who looks that this player is very well liked".
Remembering how good it felt to get my first medal, I generally like to give them to people who have few or none, provided that they've proven worthy. I think of it like this: Here is a great player whom I trust, makes me laugh, etc., but other people won't know that without getting to know him. So, I'll give him a medal, and then other people can see that at least one other player thinks well of this person.
