Well, the fact that Moneybookers has lower fee's is indeed something that pulls me towards using Moneybookers more. However, a lot of people use PayPal. Moneybookers is great because of the low fee's and you don't get headaches like you do with PayPal with the limitations, the account closures etc. Saying that, PayPal is used by nearly everyone which makes it a better form of online payment.
The payment gateway you choose depends on various factors.
1) Which methods most of your clients prefer to use
2) What is convinient for you when it comes to maintaining the account and making withdrawals.
PayPal is good if you are dealing with international clients since a lot of
people are already familiar with it. Moneybookers (Skrill) can be quite convinient
for people in regions where PayPal does not work.
Anyway, I am just wondering why you have to choose between the 2 methods. Why
can't you use both payment gateways?