When to pick Doran's shield and when to pick cloth/crystal?
(Note : the tank I pick toplane is usually shen, if that helps). I never really pick doran's shield, because I feel like the damage reduction isn't Worth it in most cases, if the champion isn't entirely/heavily AA-based and that cloth (or ruby if AP) would be better. However the opponent sometimes does a surprisingly bigger ammount of damage than what I had expected and in those cases, I always Wonder if having started with the shield would've saved me. So when is it better to start with that round wooden plank and when is it better to start with the body armor?

is stronger the more often the enemy needs to hit you, so take it against AS based champions (Teemo, Kayle) or CD based champions (Ryze)
has the distinctive advantage that it protects you from minions, which can easily do more damage than most champions. So take it when your champ needs to go deep.
, or against champs who deal primarily on-hit damage as opposed to physical damage AAers (i.e. good against
, not so good against
)