I am really leaning towards GURPS right now; the character fatality rate doesn't bother me that much because my players generally tend to be fairly smart when they do enter into combat; hopefully a new and deadlier system will just make them play that much smarter.  The learning curve isn't really that bad, but the system will be a bit different than whay my players are used to (as the majority of them are mostly familiar only with d20).

The only thing I can see confusing them is the sheer number of skills and advantages and disadvantages that GURPS has for them to choose from.  I intend to solve this with a well-developed list of templates for them to choose from to ease them into it.  I've a wide variety of cultural and occupational templates I am working over in my head now, just putting them to paper is all I lack.

There's a few GURPS books I am awaiting the arrival of that will help out quite a bit in this.  The only one I was hoping to add into the collection that I haven't yet found in print is GURPS Magic.  Kinda weird that it's GURPS 4e and out of print already...

I feel you on 4E. while I do like the system on it's own. I find the more I look at it, the more difficult it seems to be to convert my existing campaign to this system. If I do run anythign 4E, it's going to need to be made for 4E.

HERO is good, but can be a bit clunky from the GMs POV.  don't know much about GURPs. The D6 system might be good if you want a lightweight system that is easy to tinker with.

-Eli 

If you're aiming for a more 'realistic' mechanic for your setting than GURPS is best, but it does have a high character fatality rate and can have a high learning curve. As Designer/Gm you'll need to go through all the character generation stuff and make tight decisions on what is or is not being used. Luckily GURPS works well in that it doesn't fall apart if you chop out optional parts or limit what you put in.

HERO is balanced the opposite way, you can't really cut things out without breaking it.  It also does 'normal people' poorly on many levels and it can be actually hard to kill anyone/anything. Combats are long drawn out things that can take entire sessions, but work well if you want 'epic' battles.