A lot of people have trouble with paypal freezing accounts and taking the money in the accounts, I have heard loads of storys about that happening..

I dont know what propay is like because i have never used it and havent heard much about it either im afraid..
If its like paypal and people have to signup then I would think going with paypal is better, more people would already have an account and because its a bigger site people might think the security is better