I have experience on all three machines, so heres my $0.02.
I drove a JLG before they purchased Gradall and from my own experience I thought the machine was a POS :cussing . Way too many bells and whistles that didnt work, if your going to put a windshield on a forkilft at least have a windshield wiper that works. Not fun opperating with your head out the side window, and who the hell need a door on a forklift? :beatsme Not to mention a heater that blows cold air, turn signals, way to many guages. Maybe I am just used the the Southern California job site with 80 worktrucks on the road and people everywhere but I dont need to know RPM, torqe converter temp, speed, ect. They also have a european feel to them, I cant explaine it but just didnt feel right.
The Catipillars are similar to the old JLG machines as they are 4-way steering and "cushy" but have less needless items on them. They also are more nimble and more of a everyday work machine instead of a rental.
Both dont even compare to the Gradall though. The Gradall (at least my 544D-10) is the king of the construction site. Its as reliable as a battle ship, and is the machine that I judge all others by. Our company owns 34 of them and actually quit buying them when JLG bought gradall in the late '90's. The new JLG/Gradall machines are alittle weak in the lift capacity department but are more opperator friendly (I cant get over the plastic used throughout).
Hopefully the joint Cat/JLG machine will follow the saying "whats old is new again" and produce a machine that can handle anything that is thrown at it without all the bells and whistles, If I wanted a cup holder I would buy a BMW :drinkup