Alertpay is smaller and trying to make a name for its self so has good support, etc. If they ever get as big as Paypal I imagine this will disappear.
Concerning fees, I don't think Alertpay is any better really. If you only receive $400 a month or less, it's free. If over its 2.50 % + $0.25 USD. Plus they charge for adding money via creditcard an extra 3.5%.
Paypal is a better deal (at least in Europe) if you add funds to your account or link it with your bank you can send and receive money for free, and withdraw the money to your bank account within 1 hour for free. Otherwise it's 3.5% flat fee. Plus, everyone has PayPal already..
As much as I'm not a fan of Paypal, I wouldn't jump ship yet.