I like Rangers and Pathfinders well enough, and I think they are different enough that you have to make a choice about the use you intend to put them to.
The Pros: Fritz' article.
The Con: Shooting Mech. Lack of speed.
I'm not sure I would use either of these units if I were to redesign my Eldar list... which I will, eventually. The reason? In Round II Hard Boyz 2009, I was matched against another Eldar player for the win. That's a game that sticks with me, hard to shake off. My Pathfinders were worse than useless. They literally couldn't do a thing against he Wave Serpents Falcons flying across the board, ripping me apart bit by bit.
They couldn't participate in the first scrum, when battlefield dominance was being decided - they were in the backfield! When the dust settled, it was a matter of time before his tanks forced me off objectives... that, of course, being the biggest downside. Pathfinders simply can't stop a tank from shocking them off an objective. They can't even Death or Glory!
I've used Pathfinders to provide cover for my Reapers on boards with little terrain. They go to ground and block with their flimsy bodies.
Here's a use I put Rangers to that I've never seen others do: put them in Falcons. The norm is putting a 60pt unit of Dire Avengers in a Falcon to make them a scoring unit. For 35pts more you can put 5 Rangers - something that can benefit from the cover when your Falcon is blown up. By that point of the game there are usually troops on foot to shoot at.
Just some thoughts.
Is it a Warwalker or a Wraithlord? I'm poor - I build stuff that can be either. I've used this model and its two brothers for both purposes.