I can tell you from first hand experience, I have OWNED AND RAN BOTH. My Crunch blew up on me...
In short, I say get the sundown.
Here's the explanation.
I have a 15" RE MT as you can see in my sig, I was running a Crunch GP3000D-Pro for about 2 months or so, all was well and I thought it was amazing. After about 2-3 months, the Crunch blew on me. Figured maybe it was just a blown fet, so I changed out the fets. It blew again, this means there was something else blown. Maxxsonics has no online authorized retailers as far as I know, so if your buying online, your screwed. This may not be the case anymore, but I know it was true at one time.
After messing with the GP3k trying to revive it, I decided to put the extra money towards a real amp and pay a real price. I had the money at the time so figured might as well. I ended up going with the SAZ-3000D.
Now, with the sundown, my system is louder to the ear, and definitely to the car (windshields are flexing WAY more then with the crunch). Another benefit is I guess the power is cleaner, I'm not sure really but the sub runs MUCH cooler at full tilt then it did with the crunch. (gains set with a DMM, so don't come back at me with 'clipping' and nonsense.)
Not to mention the Sundown never gets past what I would call warm, even when I first hooked it up and went 2 hours on and off at full tilt, it was still just a bit over the ambient temperature. (I live in FL, I'm saying the amp's heatsink was no more then 110 degrees.) With the Crunch it would get hot enough I couldn't keep my hand on it for more then a couple seconds.
On another note, Sundown TRUMPS maxxsonics in terms of customer service. I tried going through Maxxsonics customer service, and just kept get relayed to people who couldn't help me. It reminds me of Dell tech support. Now with Jacob, I've talked to him a few times and whatnot (asked him questions via PM, email, etc) and he has always gotten back to me within 5 minutes, most of the time less then 1. And I didn't even buy anything directly from the man! He's just a good guy who loves to help and likes seeing his product being used and appreciated. (I bought my amp from Chris at dB-r.com, who also has some of the BEST customer service I've ever seen in terms of sales and warranty. Something crazy was wrong in the amp, it blew after about 10 minutes of play, he told me to send it in, he would take care of it. No questions asked, and he covered shipping, parts, and labor.)