i would say overall the JL has a better quality but the Memphis is also hase huge power amps. The largest JL is the 1000/1 which I love since its a regulated power supply with impedance from 1.5ohm to 4ohm and voltage as low as 11V. But Memphis makes quality amps too but no features really stick out to me. If you get the JL with warranty go with them, if not I'd pick whichever is cheaper.
out of expierience with both id say memphis, if you ask me its sound is way nicer, the main thing i like about JL is the power through the ohms, thats pretty sweet, but memphis
The only thing that sets JL amps apart is thier regulated power supply. They are not terribly underated. They also do well on a stock electrical system b/c they can run well at lower voltages.
they're both good, memphis is getting pricey too, jl has all the things stated above but memphis has some big models, very powerful and better than jl 1000/1. Memphis is very underrated too.