I left 2e for GURPS, Hero System (Fantasy Hero and Champion 4e) , Rolemaster, DC Heroes and trying other systems being run by friends.
I left 3e for both Savage Worlds and Mutants & Masterminds, but I would still use a house ruled 3e as a "compromise" system.
As for 4e or 5e, I have not left either given that I have not run/played them. I did download the 5e Basic Rules, the 5e SRD,and the 4e quickstart). I also bought two 4e supplements and some 3rd party 5e supplements, but not the PHB,MM or DMG for either. Both had some things that I really liked. However, for various reasons, I have decided that I would rather not use either. Despite the 5e online Basic Set convincing me that I might switch to it once the core books and supplements were released, I found that I would have to house rule the hell out of 5e and was better sticking with a house ruled 3e if needing a "compromise" edition.
Ultimately, I would rather run fantasy using Savage Worlds or, maybe, MERP or Rolemaster. I would also like to try running fantasy using Adventurers!, Barbarians of Lemuria, Cortex Classic, Pip System, Tiny Dungeons 2e, Unisystem (classic and cinematic), Atlantis: The Second Age, Earthdawn 1e, Talislanta (probably 4e), and Marvel Heroic. Finally, despite my general dislike for d100 roll under systems, I want to give Warhammer Fantasy 1e a second try as there are things that I missed in the blocks of text many years ago.
For non-fantasy, I want to run more superheroes and try Icons, Bash: UE, and Supers: Revised. I also want to give Bond 007, and Top Secret SI second looks to see if any of them can overcome by general dislike for d100 roll under (Bond 007 is a system whose design I truly admire).