I feel like Fable makes more sense, Gears games already look pretty good with BC enhancements (minus the ones left behind like UE), whereas the Fable games are a pretty inconsistent experience that need some QOL updates alongside fresh paint.
Also unlike Halo or Fable where each game is fairly different, Gears is... idk, sure each campaign is worth a playthrough but as a very casual fan there doesn't seem to be much reason to revisit horde/MP from older games, it stayed fundamentally same just with obvious additions over time, right? I'm sure a diehard will flame me for not recognizing 2 or 3 or whatever had best pvp/balancing/maps/etc but it doesn't seem quite a Halo situation where each MP had its own distinct vibe and pace to the point each has a small fanbase.
Edit: this is assuming we're getting one, if both happened, more power to everyone,, I'm not opposed to publishers keeping updated collections of classics around and don't mind the remaster-itis in the industry