I personally love War Walkers. They are a cheap formation that nobody wants to shoot at but they have to because they annoy your opponent. I've had my opponents do their best to IGNORE them but eventually had to use 1-2 activations to take them out.
A classic example of a Warwalker strategy is to bum rush titans. I did this to a couple people, the most notable was ePilgrim's Warlord titan in a 5000 point game we played. He was about to activate his titan to shoot at MY titan, so I moved the War Walkers into a crescent moon shape around him, forcing him to move back (due to my ZoC). It was either that or completely obliterate my War Walkers which would have been a waste of his activation. He ended up out of range of my Phantom except for his most extreme weapons and accomplished nothing that activation anyway. My phantom went on to destroy him outright, but I credit those little War Walkers with the kill.
I think the only reason you see Rangers taken over Walkers is because you can choose a formation cost of Rangers within 25 points. Walkers are a fixed price. Rangers are the afterthought scout formation when you can't plug anything else into the list. War Walkers IMO are the scouts of choice.
To this day this represents my favorite Epic pic of my games.

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author of Syncing Forward and other stories...It's a dog-eat-dog world, and I've got my Milkbone underwear on.