Personally, I'd use PayPal. However, if you're going to create a SaaS and are using PayPal, I highly recommend that you create a new account for the business (You are allowed 1 Personal and 1 Business account separately with PayPal[1]). The reason I say this is because, if you ever decide to sell your SaaS you cannot transfer the user subscriptions with the email to the buyer as, they are linked to the PayPal account - so you either have to give them the PayPal account or they're going to lose a lot of existing buyers (People sign up for these types of service and forget they're paying).
[1] https://cms.paypal.com/us/cgi-bin/marketingweb?cmd=_render-c....