User blog comment:TheTobarMethod/Think Twice About Guardian Angel/@comment-5877442-20130412084841

The three defensive items that can be chosen from on all ADCs are GA, QSS/MS and BV.

BV is good if they have a Blitz/heavy ccer/good initiator/a Karthus etc.

MS if they have a Zed/a heavy ccer/good initiator especially etc.

Finally GA if you have a bajillion teamfights and you feel unsafe/your team has no peeling potentional/they have 3 burst champs etc.