Epic cons:

• Filled to the brim with DRM, at the point where you can't even launch many singleplayer games offline
• Actively against linux, for some fucking reason
• Bad launcher (but this one is no biggie, you can and should use Heroic launcher instead of the official one)
• Bad store in general compared to steam
• Ties with Tencent (super anti-consumer chinese state-owned megacorp)

Epic pros:

• Free games
• With coupons prices can get VERY low
• When it opened I heard the percent they take from game devs was lower than the other stores (not sure if it's still the case and tbh if it ever was)

Steam pros:

• Pushing linux gaming like their life depends on it
• Generally correct towards the consumer
• Huge store and many information, from the game store pages to the workshop
• During sales prices are good

Steam cons:

• Drm
• Bad official app Ux and messy ui

Gog

I don't know anything besides the fact that it has drm-free games and that it's owned by CDPR (the guys who developed the witcher series and cyberpunk)

I personally purchase my games on steam, since I think their contribution to linux gaming is crucial for linux to go mainstream

Choose what you will knowing this. If someone else wants to add something to this list you're welcome to do so.