I'm not a great player but I'm kind of happy to see other people suggesting the same thing I usually preferred -- upgraded yellow trinket gives you an infinite stream of wards for 250g, and just keep a pink ward in inventory for doing an objective or whatever.
If it were platinum or above, or ranked 5's or something, I assume everyone would have red and blue trinkets, but otherwise yellow upgrade is super nice for helping out yourself and teammates.
If you're support of course you want red trinket instead once you have sightstone.