I do code review on both Gitlab and Github and found the experience on Github more pleasant. Things that help:

- Keep the PR small, the code changes focused.

- The “viewed” checkbox per file. Tick it as the file is reviewed. If the file is changed later, it will expand as “Changed since last viewed”. If not, one less thing to check on next review iteration.

- Keep discussions off Github. There should be one comment per issue as the initializer as well as reminder. The long discussions goes into a Slack thread.

- The reviewer is the one to resolve the comment. This way, you can resolve them as in “tick them off” as done.