Well, regarding ship models in styrene, this is a highly debatable question to answer! First off, it is important to remember that many of these companies have been in business for many years, and have a backlog of older kits still in production that are generally not as high quality as their newer kits. Second, it is also good to remember that even the best manufacturers will produce a bomb from time to time, and so you probably shouldn't judge the entirety of a manufacturers kits based on one dud.
So with those points in mind, I would probably rate Hasegawa as the best, for reasons of quality and variety of kits (Dragon is even better, but they don't make a lot of ship kits). Fujimi kits are excellent, and Trumpeter or Aoshima is probably third (watch out for some of the older Trumpeter kits, but their newer ones are very good). Individual kits from other manufacturers can be excellent as well (Revell has been coming out with some great stuff lately, but their older kits are pretty poor by todays standards!). I thought about mentioning Tamiya, but really, they haven't come out with much in the way of ship kits for about 25 years (but they have just released a couple this year), though they certainly were the industry leaders back then.