That's a rather vague question
What do you mean by "properly"?
If you mean traditionally, I'd say Yoshindo Yoshihara would be the best alive, but good luck getting your hands on one of his pieces, ¥3,000,000 easily.
If you mean the metalurgically soundest blades, you'd probably be looking at Angelsword. However, their methods and fittings are as non-traditional as you can get.
For a good balance, I would suggest Howard Clark. Good metalurgy, but traditional fittings.
The thing is, the traditional way of forging katana massively drives up the price, but actually decreases the performance of the blade. Folding steel purifies it, but also removes good impurities like vandium. Then, tamahagne is one of the worst sources of steel imagninable; using L-6 (like Clark) or S-7 (like Angelsword) gets better performance out of the steel for a much lower price.
If you just want Japanese steel, I would suggest SwordStore
. They have good blades available with the Japanese governent's quality regulations.