Donor 100 May be better... /God and /enchant help. As well, the one diamond a day is a Big Bang in the long run
Go easy first. Some people might not like the server, so don't waste $400, or even $100, if you aren't gonna play. I'm can't say, since I'm not donor, but donor 25, or 50 seems to work out for most people.
I suggest that you start out with getting donor50, if you like it move onto donor100, make sure that you're certainly happy with the rank before getting donor250 or 400, as, there are no refunds or transfers of ranks ^-^