Buy once cry once. Best advice I know regarding Jeep parts. I'd go for an ARB air locker. Expensive, but at least you'll never look back and say, "I should have just paid the first time."
Ahhh yes, the age-old e vs air debate.
Each system has their own set of pros/cons so I am not sure I would call one better than the other.
Plenty of people have looked back on arb's when they rip the copper tube on the inside of the diff, or after they have to deal with compressor freeze-ups in Winter, just as plenty have looked back on e locks when they burn up the electro magnet, or have to go an extra 1/2 revolution to engage them.
While air lockers are generally built tougher and usually lock up faster, they also have a lot more sideways stuff that can go wrong. They require air for example which is not only an added expense, but if ANYTHING goes wrong with the air system.... no lockers.
E-lockers are usually slower to activate and are (generally) not quite as tough, but they are a more compact system which doesn't rely on a lot of sideways equipment to operate, maintain and upkeep.
Long story short... they both have their pros/cons and therefore which system is "better" completely depends on the situation.