Short answer: set up Alipay first, WeChat Pay as backup. Both are accepted at the vast majority of shops, both take foreign cards, and having two means one failed payment never strands you.
Side by side
- Setup: Alipay is usually simpler for foreigners; WeChat may ask an existing user to verify your new account.
- English: both have English interfaces; Alipay's tourist features are easier to find.
- Acceptance: both near-universal in cities; some small vendors show only one code.
- Getting around: Alipay has Didi taxis built in and metro codes in many cities; WeChat has mini-programs for the same.
- Fees: similar — small payments generally free on the platform side, larger ones around 3%.
- Extras: WeChat is also how Chinese people message — useful for contacting guides, hotels and new friends.
Recommendation
Install both before you fly, link the same card (or two different ones), and run a ¥10 (less than $2) test with each using the card on this page.