I've used BankDirect.com for about a year now, and am very happy with them. They offer more bonus miles than Guaranty bank does (signing up, direct deposit, auto payments, and a couple others). They offer the same number of miles/month as Guaranty bank does. B/c of the add'l bonus miles with BankDirect, I think it's the better of the two.
If you decide to go with BankDirect, let me know. If I refer you, we both get 1,000 bonus miles.