Iceborn Gauntlet is significantly more popular on him because it's way cheaper (allows you to get your muramana+botrk powerspike faster), and allows you to kite with permaslows, while trinity is just a bit more damage. Of course, if you're against a full AP team comp and you don't need armor, go trinity.
Hey bud, so Iceborn is best against comps that are full AD, and you have have a heavy frontline, like a tank or 2. Because you will have to be in the fight just like everyone else. More utility with the slows, and more HP so you are not as squishy. Trinity Force is a safe option against comps that are well balanced, HP/amor stacking, AP, AD, and engage supports or encharters. Trinity allows you to play a fast game, move speed, attack speed, and decent damage. In my opinion it comes down to prefered playstyle. trinity force benefits when you keep your passive up and AA in between using your low cooldown abilities. If you prefer the poke style Ezreal, just using your Q/W/E combos then lethality is better, but you are more squishy so your methic then becomes super important.. There are some awesome guides out there, Ace_Ezreal and Dragdar are my two favorite Content creators for ezreal builds, guides, runes, and playstyles. Check dem out!
Iceborn Gauntlet is significantly more popular on him because it's way cheaper (allows you to get your muramana+botrk powerspike faster), and allows you to kite with permaslows, while trinity is just a bit more damage. Of course, if you're against a full AP team comp and you don't need armor, go trinity.