A customer wished to include an option to accept payments by PayPal alongside Actinic Payments which caused me some head scratching on the options. What I'm about to write here is my understanding now of the difference between PayPal Express Checkout and PayPal Website Payments. -This may well not be news to you, but would have saved me a bit of time 
PayPal Express Checkout takes the customer directly to their PayPal account to finalise their order and payment. The PayPal EC might typically be added to the 'Show Cart' and or early checkout page.
Adding PayPal Website Payments provides a choice at a late stage in checkout, where the customer will choose between the alternative payment systems offered. (In my case between 'Secure Card Payment via Actinic' and 'PayPal Website Payments')
There is a further option of the PayPal Website Pro facility which I have not used.
PayPal Express Checkout takes the customer directly to their PayPal account to finalise their order and payment. The PayPal EC might typically be added to the 'Show Cart' and or early checkout page.
Adding PayPal Website Payments provides a choice at a late stage in checkout, where the customer will choose between the alternative payment systems offered. (In my case between 'Secure Card Payment via Actinic' and 'PayPal Website Payments')
There is a further option of the PayPal Website Pro facility which I have not used.