In prod replication agents, which user we should user, I tried using Replication user, with replication permissions, but i was facing some issues, and we started using admin user.
Please suggest me which is the better approach.
If you are not having multi locale website(like for china,india,us etc) and want to replicate the content from author to all publish servers use replication receiver as the transport user.
If you want your content to be replicated only to limited locale then you can create separate replication users and provide the appropriate permission on content.
you could use the "replication-receiver" user for your replication agents. In order to use this user, you need to enable the user on the publish instance(set a password for the user), then configure your replication agent, to use the user replication user with the password previously set.