I know the Katana is sharp enough to cut through stuff that a machette and hatchett wont.
You are talking here about two entirely different construction processes and material choices which is a result of very different use. Comparing them is as pointless as comparing which is the deadlier, a shark or a lion. Well, in the ocean, I'm going to give the edge to the shark. On land, however... Understand? You would not be using a sword for the same purposes that a machette or hatchet would be used for, and by the same token you wouldn't use a hatchet where a sword is demanded.
I also know it never needs sharpening.
Now where on earth did you get that from? They aren't Wiltshire Stay-Sharps, you know. The process of sharpening a katana is polishing, and if a sword is used frequently, it is advised that it undergoes regular polishing as well. It also takes out small nicks and chips in the blade as needed, as well as giving it back it's ever-so-pretty appearance.
Who makes the absolute best Katana that will stand up to hard use?
Oh, that's easy. A top level traditionally trained swordsmith, such as Gasshan (designated a National Living Treasure in Japan). Got a spare $50,000+?
But really, what are you doing that you class as "hard use"? From your posts you have no experience with Ninjutsu or any Japanese Sword Art, instead you seem to have a rather naive fascination with it at present, and that is all. Find a school, study for a few years, and realise that what you are asking for here is not what you will need or want at all.
To explain, most swordsmanship in the Bujinkan (as that has been your focus of your posting) is done with Bokken (wooden swords) or Fukuro Shinai (leather covered bamboo swords). And most swordsmanship is based on two-person training exercises (kata), and is highly focused on evasive cutting (in other words, not blocking the other persons sword, as that can lead to damaging your own blade, as well as other reasons). Some schools may allow some form of cutting, but that is rarer rather than the norm. I suggest checking out the videos that Bob has put up in the Armoury section, particularly the one on the "Ninja Blog" one... then make sure you read the critique offered afterwards. Swordsmanship is not the focus of the Bujinkan, and that shows in quite a few places.
What swords are allowed to be used in Ninjitsu?
Okay, mentioned this before, but it seems it's not a typo for you. It's not ninjitsu, it's ninjutsu. The word "ninjitsu" is used by the less-legit people out there out of ignorance, to avoid looking like one of them, I recommend spelling it correctly. So you know, they are not the same word pronounced differently, they are completely different words, with different meanings and different written characters ("jitsu" meaning "truth", and "jutsu" meaning "practical art or skill"... although those who pronounce/spell it ninjitsu universally use the "jutsu" character, simply showing they have no idea what they are talking about).
As for what ones are "allowed" to be used, not really sure you understand things here. The sword used in training Japanese sword arts is a bokken, a wooden training sword shaped like a katana. There are also short sword versions, known as kodachi (short sword/tachi) or wakizashi (mounted on the side/side arm) predominantly, and again there are bokken forms of these. Additionally, you may sometimes use a Togakure Ryu sword, which is a shorter blade with a regular tsuka/handle and saya/scabbard. There is no such thing as a sword that is "allowed" or "disallowed", just the proper tools for training. Join a school, train, learn, and do as instructed there.
as in names? Who makes the best Ninja sword out there?
Why? You still haven't answered that question, I notice, although I've asked it a few times already. Without training in the art, what good would it do you? I could point you to a number of people, but it's completely moot if you're not training in the system. And odds are that you will rarely, if ever, deal with the Togakure Ryu Bikenjutsu kata, which is the only time, really, that a "ninja sword" would be used in class.... and that sword is the one I mentioned above, it does not have a straight blade, a square tsuba, it isn't worn on the back, or any other hollywood myth. It's really just a katana with slightly different dimentions.
IF you train then you will use a bokken. And maybe after a number of years (even decades or more) you may decide you want to get a metal blade. But maybe not. Rushing ahead is pointless, as you will not have the requisite knowledge to make a halfway decent selection, let alone have an actual use for it other than admiring it's shininess, and if that is all you want, then a good one is not needed.
Other than the shorter length that allows you to get it out faster; are there any other advantages to a ninja sword over a Katana?
It is a katana. Forget about any distinctions. Katana just means sword, anyway. As to advantages in different dimentions, join a school, train, study, and learn. You currently have no baseline that you can compare with, so anything that could be said is rather pointless.
Is the ninja sword which has the longer handle to appear like a Katana accepted by Mater Hatsummi?
Join a school, train, study, then ask your instructor what they allow in their school. Forget what Hatsumi "accepts", he isn't really concerned with what someone outside of his dojo is doing.
Who makes the best training Katana, Ninja sword, and bo staff?
There is no point giving you a list of suppliers unless you are training, and even then the standard answer is "ask your instructor". That's not us being difficult, it's that some instructors have very particular requirements as to what is used in their schools, or have certain preferences. Some will insist that you get everything through them (I, for instance, don't insist, but do strongly recommend it, and won't allow weapons to be used without me inspecting them first).
Your first step is simple. If you are really interested in studying these arts (really, though, it's coming across to me as a mild infatuation, rather than a true interest, kind of like a crush on someone you haven't met) then find a school, join, train, study, and learn. These questions are not really going to help you. Join a school first.
