I can't speak for other companies, but the DC alternator I bought last year has been a great product.
My RAV4 alt started as a Denso HO alt for a 4Runner V6. Swapped the pulley and the rectifier/regulator circuits. It fit perfectly and there was no wiring to do. I'm able to power my competition system almost exclusively using alternator power (so I stay at 14 V during the runs).
As others have mentioned, it's a little more expensive and takes a couple weeks to deliver. They do start with a new product and add to it, rather than remanufacture old ones (replace brushes, circuitry, grease the bearings, and clean the terminal).
It has developed a light squeak in a year's time... but considering how hard I push it, that's not bad.