My guild started in Line but after a few months, all of us moved to Discord and I really prefer Discord. For Discord, the ability to make separate channels and limit who can post is great, as well as the the ability to make tags for groups (back when tank first launched, we even had a chirpatine tag so all guild members who could run chirpatine would know when P3 opened to attack). You can also use bots in Discord for reminders. I also like the ability to edit what you wrote and if you have administrator power, the ability to delete other people's posts. You can also see when people in the chat are online easily.