Based on our record, Uplay should be more popular than Game Center. It has been mentiond 2 times since March 2021. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
For Rainbow Six Siege, you will need to link your Uplay account. If you do not have one, create one for free here: https://uplay.ubisoft.com. Source: over 2 years ago
"2.1 Creation of your Account. You will need to create a UBISOFT account (an “Account”) to access and use certain Services. You can create at https://uplay.ubisoft.com/, by supplying a valid e-mail address, truthful and accurate information, and all the necessary criteria. Source: about 3 years ago
u/JTostitos is right though that Game Center was designed for this although it has gone out of style with many game studios lately. But it all depends on how the game is designed... If you require constant client-server communications then implementing Game Center doesn't really make sense when you can easily roll your own leaderboard on the server. Source: almost 2 years ago
Origin - Origin is your new digital playground. It’s where you go to find the best that EA has to offer.
Nakama - Nakama is an open-source distributed social and realtime server for games and apps.
Epic Games - Computer game storefront that gives 88% of revenue to developers
Armor Games - Play free online games at Armor Games! We're the best online games website, featuring shooting games, puzzle games, strategy games, war games, and much more...
itch.io - An online game marketplace and community.
Kongregate - Kongregate has free games that you can play online. Choose from thousands of free flash games.