There are several qualities that individually or in combination might justify describing a watch brand being described as "best". Some could be:
1) Technical superiority of the movement
2) Innovations in movement design and functions
3) Case design
4) Finishing of the movement and case
5) How comfortable is it to wear?
6) Layout of the dial - overall beauty, legibility, etc.
7) Is it top value compared to the cost?
8) How well does it hold its value (sooner or later you might want to let it go)?
9) If you want to let it go, is there a large market for pre-owned versions so you can find a ready buyer?
10) Durability. Related to durability is how often does it need to be serviced? Related to that is cost of service. Related to that is the quality of the service (does the watch come back working perfectly and cosmetically looking the way you want it to look)? Related to that is, do they have a consumer friendly service center(s)?
11) Does it fulfill its objective as being the ultimate sport or dress (or other function) watch?
12) History of the company. Related to that is, will they be around in 20-30 years?
13) By far, the most important is, what watch makes you the most happy when you wear it?
For me the 2 companies that hit the most of the most important criteria are Rolex and Patek. Consequently I own a few Rolexes. But, the watch that sings to me and from which I derive the greatest enjoyment is Patek.
Best,
patekova