These are my opinions, I hope they are not taken as edition bashing... they are simply my tastes.
3.5/Pathfinder: I've found this rules sets very complex to DM, it takes much more time to plan, and limits my ability to DM "on the fly" (the manner I prefer to DM, it allows me to let players explore what they want more easily). The granularity of the options in this rules set does give a lot of mechanically aligned flavor, but sometimes details are so complex that it slows game play (via cross referencing in the rules). I am sure that once you have played using this rules set for a number of months it becomes easier (much like mastering a video game like Starcraft), but I'm an older guy with less time on my hands, I want to get into the game easily and also use rules that allow new players to pick up the basics quickly so we can focus on the storyline. One cure for this is adventure paths, but if I accept that as my best option based on the rules set, then I also accept that I run stories written by other people... that means I lose my favourite part of DMing.
4th Edition: Disassociated mechanics are odd, whether that term is accurate or not, who knows. To explain further, when a Mage has a mechanic called "Blink" (minor teleport), and a Rogue has a "Quickstealth" ability which does the exact same thing... then I feel the pursuit of balance has sacrificed flavor to achieve it's goals. This quickly made me feel that I could just assume an "optimized character build" and no matter what my class or race I would have the same chance to hit using my chosen method, do essentially the same damage, etc. etc. In addition to this, the flavor of this edition felt wrong for me, terminology like "powers" and mechanical descriptions which evoke video game special effects as opposed to LOTR or Conan didn't really help me imagine world I wanted to create, or play in.
Also, both systems do not discourage "role play" (again, if that can even be defined clearly), but both systems do focus heavily on mechanics. I prefer simple broad mechanics that allow myself and my players to define and execute our own strategum based on circumstance, as opposed to finding the optimal preset combo for a given encounter.
Example: Can my Paladin use a Holy Strike Feat or Power versus some evil Orcs, sure... the rules tell me to do it, it damages Evil creatures optimally... but I often find when I play a more open game, my players may lure the Orcs onto a ridge and start a landslide knocking the Orcs off the cliff... they may try and dupe the Orcs by impersonating their Evil Diety using fog and a cow horn to their advantage... they may realise this type of Orc is Lawful Evil and challenge the leader to Single Combat.
The other rules sets mentioned do not ban this type of play, but neither really focuses on it either. Once you delve too deeply into the pit that is fiddly mechanics, I think you may lose some potential for thinking outside of these mechanics and creating an engaging quirky, comical and very unique game for your players.
What I like about role playing is the freedom to adventure... to few rules or to simplistic rules can break suspension of disbelief... many and overly detailed rules can lead to a "mathy" focus (generally saying "look at the math options", not "look at the situational options").
I think the various editions have given us many cool things... I think each edition has also changed the focus of play. I am well aware of where I want my game focus to be... the other styles of play I have mentioned are not wrong, nor are they "not fun"... but I prefer a DMing simple rules set and giving as much freedom to players as possible. To achieve this, I have customized my particular game to focus on these goals... since my final goal is to have fun with friends.
In closing... I have no preference... I will steal good ideas from any game
