I'm interested in a V8 JK and i haven't decided on what engine swap (Hemi Vs LS). I read that LS engines have a reputation of cracking engine heads and eat valves. Also when comparing stock engines hp/tq, i found that HEMIs out perform LSs (except for LSX). On the other hand,HEMIs are overpriced and heavy. Beside some people complain that the Hemi swap output is below expectation.
I'm looking for a fast 0-60 JK with some off-road capability (keeping the front axle)
Properly installed it's unlikely you will have a mechanical failure with either engine. The Jeep electronics are the most likely thing to fail. The LS does have the option to run in a stand alone mode if the Jeep network goes down.
Most Gen IV LS truck engines do not run an EGR valve if that is what you are referring to.
The LS is smaller, lighter and easier to cool. Less mods to the chassis and suspension are required with the LS. The Hemi enjoys better can bus integration with the JK making the electronic interface easier.
If using an automatic the 6 speed GM transmission is superior to the Chrysler counterpart. Much of the LS's mileage and performance is due to the transmission.
Either engine will support the hp you desire. The LS can be had in stock form from about 300 to over 600hp.
Base your decision on cost, availability of replacement parts, mileage, weight, ease of installation, ease of tuning, integration, and other factors.
I have a secure feeling with the LS in a JK when I'm wheeling. I know the TIPM could fail and I would keep going. It's a very simple engine with very reliable electronics. The LS has several self protection modes. A couple years ago I had a customer drive an aluminum LS 5.3 off a mountain in summer running at over 275 degrees when his cooling fan failed, it went into a reduced power mode. That LS still runs great today.