I hate collectibles that are a hassle to get. GTA and Assassin's Creed are the worst offenders IMHO. They require you to litteraly comb the whole map in order to find them all. The only difficulty is how tedious it is to find them.
I like collectibles that are interesting to find and/or do not feel like a chore. Such as :
- The Super Mario games (World and modern) and their special coins to get in each level. They're interesting to find because they often require you to think out of the box or go out of your way to get them. And even if you do not get them in your first playthrough, knowing that they are divided to only 3 per level eases the task and it doesn't get tedious.
- Likewise, Crash Bandicoot and Spyro the Dragoon collectibles. They often require more of an interaction from the player than simply walking over them. Spyro can be a little frustrating at time though becausue gems can be tricky to get. But like Mario, they are separated by levels which aren't that big.
- Gwent cards from Witcher 3. There are a lot, which are obtainable by various means : buying them, winning them, getting them from sidequests. They are good collectibles because they are interesting to get, by various means, there are sidequests and stories attached to them.
- Not everyone will agree but Riddler trophies in the Arkham series when they are indicated on the map. The challenge here is to solve the riddle, not really finding them.
- Party members in the Suikoden series. They actually add to the game.
- Orbs in Crackdown, because there is a sound effect cue to finding them.