Looks:
I personally find the JL HD amps to look much better (more mature/look much better in cars). The JL amps match cars much better than a ZED with "nifty" lights and design.
Customer Service:
JL audio has amazing customer support. I have dealt with them many times. The owner of ZED audio is very strong opinioned to say the least. I would be very worried about ever having a warranty claim with ZED knowing they don't have the financial capital support and market share that JL has.
Power/Sound Quality:
If anyone doubts JL HD amps in sound quality, check out actual MECA/IASCA competition winners. I have been to several meets/competitions where all of the BEST sounding cars (both in my opinion and those that have won). Take for instance a few years back JL Audio HD amps and the C5 set won the extreme/master class.
I have owned and have several friends that have owned ZED Leviathans. Granted, we had the first few versions, but it was a PAIN to get ZED to fix the amps. They had several noise issues that you really couldn't really fix. It was very reminiscent of the original alpine PDX amps. I also DO NOT like the way the Leviathan's wiring layouts work. Speaker Wires and power on one side, and rca's on the other. Pain in the *** really most of the time when you want to hide wires, or work on less flashy builds. I'm sure now ZED has cleaned up much of their amps to work much smoother, but still it's not enough for me to sway away from them. I know more people that have switched from ZED than have kept them.
Many people hate on JL with the unanimous "it's overpriced". I guarantee you most of those people have never owned any of the products. In car audio, you get what you pay for. The JL Audio build quality in their W7 and HD amp lines are top notch. I HAVE owned the JL Audio HD amps, the slash amps, W6's, W7's. They are all GREAT products, and worth it IF YOU can appreciate everything that embodies the products. I have NEVER had any dissatisfied friends that i have prescribed JL Audio W7's and HD amps. If you are wondering what I have to reference all this, I have OWNED everything from Hertz amps, Boston Acoustics Pro's, Alpine Type-X, Hertz HX/Mille subs, and a multitude of Audison products. I used to have an Audison Thesis 3-way setup. I have come a long way of losing money from buying and trying things out all sorts of car audio. I STILL own an Audison LRx 5.1k. IMHO the only other brand worth comparing to JL Audio is Audison. I am switching from my Audison LRx 5.1k because I could not fit it in my stealth 370z build.
Don't get caught up in the number game of WATTS and specs.
At the end of the day, amps as nice as the ZED and JL HD still only show their true qualities when paired with a nice active processor. EG: Pioneer DEX-P99RS, Audison Bitone or Bitten, and the Mosconi 6to8.
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