There are a lot of other things besides power ratings that make one amp different/better than another. Damping factor, build quality, reliability, connections, features, configurations, flexibility, support, etc etc.
JL support is amazing. The manuals they come with are better than anything I've ever seen. Even their website is incredibly detailed and helpful.
JL has a long-standing reputation for being one of the best. Their R&D, design, engineering, etc is leaps and bounds better than anything you'll get with cheap stuff. They invested the time, money, and energy on the front end to release a fantastic, cutting edge, unique product. By the time it is available to you, it cost more because of this. A lot of companies can slap some stuff together and throw a number on it and call it an amp and charge a lot less money for it.
Have you seen the JL Slash amps? They have knobs and buttons for days. They aren't just for the bling factor, either. Everything is very functional.
Personally, my favorite things about the JL amps are:
1) They make their rated power at as little as 11.5 volts. The standard is for amps to be rated at 14.4v, and when they get below that, most will start to make a lot less power. So when your bass hits, and your lights dim, and your voltage drops, the amp makes less power (sometimes a LOT less) and you get less output. Unless you have a pretty advanced electrical system, your voltage with the volume cranked isn't going to hold 14.4v. With a JL amp, it doesn't matter.
2) It makes the same power with a range of loads. 2 ohm, 4 ohm, it doesn't matter. It just makes things simpler and gives you flexibility to change things up if you add or remove speakers.
Is that a good enough answer? If you need more, you could do your own research. Go to each company's website and click around. Absorb info. See what you think.
A lot of people say JL is overpriced, but I disagree. Either you can afford it, or you can't. There is pricier stuff out there. For all the things I mentioned in this post, the JL stuff is worth every penny. With rare exception, you will find most people that run their stuff will tell you that same thing. No regrets. No disappointments.