For me E3 is the most interesting out of those things, i love it for all the streams, where xbox, playstation, ea, ubisoft and so on showing off there (new) Games and all that stuff.
And Gamescomen is more like a Youtuberevent, im from Germany i could easily go there if i want, but all from a German Standpoint of view (at least for me), Gamescom is for all the Youtuber and their Fans to meet them and all that stuff. I have zero Interest in Gamescom, except if there are "Press-Conferences" like E3, thats what i care about and love each and single Year to watch all the streams 24/7 and get excited about new Game announcments. :D