I just implemented Stripe and Paypal into my site. God PayPal's entire API and documentation are beyond terrible. It's hard to put into words how bad the experience was with PayPal. It's like they hate developers or something.
I've also had a lot of clients that used paypal to sell stuff. Paypal hated them too.
Also, much of the complaining about Paypal seems to be in the form "I violated Paypal's ToS, and then they closed my account." Well, maybe you should read all those legal documents before entering into a business agreement?
The payment processing part seems to be great until it goes wrong but when it does they have the minimal resource possible devoted to dealing with it.