I don't know what the difference in update frequency is between gog and steam but I don't think it would be that big.

Q: If I buy the game on GOG can I play with my friend who owns the game on Steam? How about if I play on PC and my friend plays on Stadia?

A: "Direct Connect" (yes) is possible between platforms - but all players must be on the same patch number in order for it to work. Note that in the first few weeks of Early Access there may be some minor version discrepancy between platforms as we move to fix and address issues rapidly, and in these cases you won't be able to play between 'stores'. Ultimately, you will.

Link

I am literally downloading the game on GOG as I post. This is always a difficult decision for me, because overall, I think Steam is probably more feature rich. Having said that, I really only use the basic features so that comment may be unfair or uninformed. I choose GOG when I can, as I just prefer their philosophy on DRM, game ownership and returns. It just 'feels' more respectful to gamers.

I've changed my mind, and I will NOT be purchasing Baldur's Gate III. If Larian chooses to make fantasy RPGs not related to Dungeons & Dragons, I'll consider those, but I'm not buying anything connected with WotC ever again. After hearing how WotC screwed over the Dragonlance authors, Larian may really want to reconsider their relationship with them.

Already bought it on GoG. The Canuck in me has a habit of rooting for the underdog. It also sort of feels right. I buy certain games on the Switch (like side-scrollers) because I feel like they belong on a Nintendo console. I'm like that with GoG too. Some games just feel more at home here. It might not matter if the game in question was some kind of Call of Duty thing, but BG3 is picking up a legacy. One Steam didn't care about until the Enhanced Editions were released.

*If* I buy the game I will wait for several reasons:
1. for indepent objective reviews to be available
2. for all the inevitable bugs to get fixed
3. for a big discount

I already bought it on GOG, I no longer have a steam account

a) Because I dont have to run GOG Galaxy to run the game (You don't even have to run the games own launcher either, just run Baldurs Gate 3\Bin\BG3.exe (right click and send a shortcut to desktop for convenience) and load up your game - Although I think you have to run the games own launcher (Baldurs Gate 3\Launcher\LariLauncher.exe) if you want the online / multiplayer aspects of the game, not sure, I didn't even create a Larian Account for BG3).

b) I can download any game I purchase on GOG by grabbing the Offline Installation files, so one day when the company goes bust / bought out by someone with new policies we may not approve of / or whatever crap happens in future and GOG Galaxy client is dead as a Dodo - I still have a physical copy of the game I bought to install whenever, and not be reliant on possibly extinct online services and servers.