Always consider your team composition, the enemy team's composition, and your role in fights to determine which item best suits the situation.
Consider level of crowd control.

+ Guardian Angel when looking for a defensive option that provides a second life, suitable for diving and engaging fights

+ Randuin's Omen for increased survivability against critical strike and basic attack-heavy compositions.

+ Jak'Sho when facing balanced physical and magic damage threats in team fights.

+ Mercurial Scimitar when facing heavy crowd control threats, providing both offensive and defensive benefits with the active ability

+ Bloodthirster when you need lifesteal for sustain and prefer a more offensive build.

+ Phantom Dancer for a combination of offensive and defensive stats, especially when dealing with champions that require kiting. Potentially MS is a defensive or offensive option dependant on situation.

+ Kraken Slayer when focusing on sustained damage and dealing with tanky opponents.

+ Kaenic Rookern when facing heavy magic damage threats on the enemy team.

+ Wit's End when facing magic damage threats, as it provides magic resistance, attack speed, and bonus on-hit magic damage.

+ Serpent's Fang when the enemy team has champions relying on shields. It is a cost-effective option with a focus on shield reduction.

+ Mortal Reminder when facing enemy champions with significant healing or sustain, such as Soraka or champions with built-in lifesteal.