Hiya,
You've come upon one of the most famous debates in the Nihonto world.
Are the best blades made by today's smiths in Japan as good or better than the best of the old?
Frankly, we don't know. Shinto, Shinshinto, and Shinsakuto often have very "tight" steel, few or no flaws and very tight patterning. Some people feel these are attributes that make for the best swords.
Older koto blades, particularly those from the late Kamakura period (around 1300) have been thought by many to be the greatest swords ever made. Obviously, many of the most famous smiths in existence lived and worked in this period. There are supporters of old Koto pieces who argue that there are aesthetic qualities in the oldest swords that nobody has achieved since that "pinnacle" of swordmaking. I can't be certain, since there are so many swords being made, and modern swordsmiths trying very hard to recreate the works of old and do justice to the masters of the past. However, since we don't know their exact techniques, we are still "feeling in the dark" to figure out how they were able to do what they did.
You mention Masamune. His name was Goro Nyudo Masamune and he was one of the pioneers in the emerging Soshu style of swordmaking in that time. Much of Masamune's fame came from being favored by a Shogunate family later on, not necessarily from being perfect in every way when he first made them. Some people feel his work is among the best Japanese swords have ever been, and many others feel differently. It is thought that he was one of the earliest makers to utilize post-hardening temper to alleviate stresses on sword edges. Even if he wasn't the greatest (which he very well could have been), he was an important pioneer.
Another point of debate is laminates. Some feel that the best swords did not really utilize the cored lamination techniques found on more common pieces (honsanmai, kobuse, etc). The idea behind the lamination technique was to be economically efficient while making a sword that might bend like taffy, but won't break easily. Remember that not all steel was very high carbon or high quality, and not everyone had a large amount of the premium steel. Optimally, you would want the entire thing to be fairly high carbon, but if that's not the result from forge welding a lot of iron/mild steel with some high carbon steel, a laminate is a good compromise.
In terms of cutting effectiveness, the best measure we have does not include the greatest Koto blades. There was a book written in 1815 by Yamada Asaemon Yoshitoshi that measured cutting effectiveness of over 150 swords. They were divided into 4 ranks: Saijo O-Wazamono (best), O-Wazamono(Great), Ryo-Wazamono(Very Good), and Wazamono(Good). Some believe that the best swords of Masamune, Norishige, Sadamune, Chogi, and others would warrant a slot above Saijo O-Wazamono. We simply don't know, because they haven't been tested in the same way. The same goes for modern swords. To claim modern swords are inherently superior gives no credit to the makers in generations past, just as claiming that the old blades can never be rivaled in quality gives no credit to the heart and soul some of today's makers put into their pursuit of improvement.
The western sword world has a lot more freedom than Japan does now in swordmaking, so we can explore outside of what they are normally limited to. The consistency of the high quality steel we get is very beneficial, and the accuracy of the temperatures we can get with heat treating equipment is consistent and precise. This makes it easier to make high quality swords more consistently. New developments like Clark's Bainite-Martensite swords offer a level of durability previously unheard of. I feel that for the swordsman, some western blades offer greater value for a high quality piece than can be ordered from Japan now.
As far as naming famous Japanese makers...there are too many smiths for me to mention without forgetting some. There were a lot.
