Permanent or Temporary donation ranks?

Hey guys! I'm setting up my paid ranks for my server, and I'm just wondering what I should do. I'm stuck between having lifetime or subscription based ranks. Here's how I see it

Permanent
Pros

• Encourages people to donate more

Cons

• Anyone who donates will eventually reach the highest rank, meaning they likely won't donate again

Subscription
Pros

• Keeps people who can donate, donating

Cons

• Probably deters people from donating...

Permanent or Temporary donation ranks?