Theres absolutely nothing wrong with the 4. It's a solid knife that works hard. I just like the shape of the PR4 a little better. An easy modification of added liners or upgrading the scales (they are a touch too thin) and the knife would be perfect. Even with the thinner scales it feels great in hand.
It is hard for me to choose between the 2. Out of the box and ready to use I would chose the 4 over the the PR4. Like I’ve mentioned before the scales are my only real issue with the PR4. Based on sheaths I am a fan of kydex or plastic over leather so the 4 wins there. Blade shape, handle shape, lack of coating, squared spine and a few other small items make the PR4 the winner there. All that said it makes it hard to choose. In the end i go back to whether it is straight out of the box or had adjustments. Out of box ESEE 4 is the winner Out of the box with a few alterations I would take the PR4 over most of the ESEE line.
The biggest reason I'm going with the original 4, is I already own it. Also I have invested a bit of time and money in making it mine. This, and I finally pulled my head out of my derriere and discovered that I really don't need to buy every new knife that comes along, although I'd still like to.