Guardian Angel or Zhonyas Hourglass as a defensive item on AD Tristana
Hi all, just wondering something about defensive itemization for 
As I'm sure most people here know, auto-attack focused champions like Tristana can only afford 1 defensive item without killing their damage potential. Played her last night with the standard GA as my defensive. However, GA's cooldown is so oppressively long, it got irritating.
Looking at the AP scalings on her E and R, I started to wonder if Zhonyas might be a better defensive item for her than GA. Same general result (temporary invulnerability under fire), but available at my direct control, shorter cooldown, and the Ability Power would bump up her E's AOE damage and her R's shotgun blast.
Haven't tried it yet, just curious. Thoughts?