Ok ppl. Diffrent RPG systems have thier diffrent strenghts and weakness. Design goals and focus. Each of them having thier own merits.. These is what I think.. from what I've seen..

DnD 3rd Edition (WotC)
for being the first RPG system I've played and thus am familiar with the "feel" of it. Luckly there is the free SRD to work with.

Simply Role Playing (Microtactix)
For teaching me the joys of simple roleplaying system can be fun! and it's free!

Warhammer Quest (GamesWorkshop)
I just love the "board game" feel of this game.

Donjon
http://www.anvilwerks.com/docs/donjon
I really havent seen it in action. But its supposedly puts the story into the hands of the players.  Still have to get me a copy. (PDF)

PLAYER: "I search for a +3 vs undead dagger!"
<DM rolls dice>
DM: You found one!

Fungeon
http://www.harlekin-maus.com/games/fungeon/fungeon.html
a free game that has a really cool DMless system.

GURPs lite (Steve Jackson) Free
modular unrestricted character... COOL! classless..

The "system" I am going to play with is a mix of these games.. Rules are there to manage and make things fair. But we mustn't forget the FUN!

I think I mentioned it before, but I do like Gurps, though recently that has been for the outstanding source material in its world books.  As of the last couple of months, I've dived head-first into Simply Roleplaying from Micotactix.  It has many similarities to GURPS but is far easier to use.  It is also easily ported to mass-combat battles using their own Budget Battlefield rules, as both systems (and Compact Combat for super-detailed fights) are based on Greg Poehlein's PlainLabel game system.  The only drawback is that all that's available for Simply Roleplaying is the core rules and a weapon supplement.

I'm working on several SR supplements for my own use and possibly a web-page.  One of those things is adapting Steve Jackson Games' Transhuman Space setting to SR.  It's a fun setting, but the very complex nature of creating 200 pt GURPS characters makes it a drag to implement.  Not to mention the really aggravating and detailed firearms combat  system.  And don't even get me started with the Starship Design Rules.  You need a PhD in mathematics to design one of those things.  

But that's just an example of what I'm doing with SR and how flexible it is if you don't mind doing a little conversion work.

As far as D&D goes... well, I've been gaming for 15 years, and I started gaming with the old D&D Basic Set (red box) and moved to First Edition AD&D a year later.  After that I played Second Edition for a long time.  Then, I moved on to other systems like Earthdawn and Gurps.  Third Edition just doesn't do it for me anymore.