Moving from PayPal Standard to anything is pretty easy since for most people it's a very simple payment service.
The other gateways are more complex since you cannot migrate the credit cards, and if you have recurring profiles managed on the gateway, you will have a harder time moving as you'll have to convince your customers to punch in their credit card again.
The other gateways are more complex since you cannot migrate the credit cards, and if you have recurring profiles managed on the gateway, you will have a harder time moving as you'll have to convince your customers to punch in their credit card again.