I'm not very knowledgeable about traditional Japanese knives.
The two most knowledgeable people about yanagi and deba I know who contribute online (blw and KC) do so at Fred's Cutlery Forum, but neither is very active right now. You might as well register and raise the question there, but you're going to get as much noise back as real information. There are some good people on the Knife Forum. As always, the trick is separating the wheat from the chaff.
If you want to know why some knives are better than others, I probably know enough to discuss that insofar as the more popular knives. If you want to know the basics of sharpening them, I know the basics but just the flat-bevel basics. My experience is limited and old.
Good yanagibas are expensive, but excellence starts at around $300 with a knife like the Masamoto KK 300. When you spend substantially more you're buying things other than pure performance. Mostly prestige. At a certain level of quality the primary differences between knives is sharpening. As a practical matter, a properly sharpened, $1,000 aogami #1 honyaki won't cut any better than a properly sharpened, $300, shirogami #2 kasumi.
To the limits of my knowledge if you buy stainless, you're buying at the very low end and stainless isn't worth even the relatively low investment unless you're buying for fun. Based on my admittedly limited experience I strongly recommend against buying a Global yanagiba.
As a purely practical matter, mostly for reasons of price and sharpening, I think a Konosuke 300mm White #2 suji would serve better than any yanagiba for portioning fish as well as general slicing.
A LOT of good sushi men use sujihikas during the day and bring out the yanagibas at night for the dinner crowd. If you think I'm telling you that a yanagiba is part propaganda, you're right. If you're going to get serious about using a yanagiba, you want to learn the deba too. They are a team.
Like the day time sushi men, I use a gyuto and suji for medium and small fish fabrication. I used to use a butcher's instead of a gyuto or deba breaking big fish like an Asian fish market, but I don't do big fish.
If you're asking which yanagi to buy for yourself, get a Masamoto KK.