Stripe is fairly straight to set up if you sell products in the US and only accept cards.

For selling a SaaS worldwide, Stripe quickly becomes just as much of a nightmare. Taxes, billing, chargebacks, subscriptions, web hooks, different payment methods, VAT validation, card expiries, legislation, changing laws, SCA flows, and my favourite: SCA iframes that become non-responsive on browsers in a certain language. It is a never ending source of edge cases.

Don't ask me how I know... My biggest mistake with my business was that I vastly underestimated how much work it is to accept payments. In my case, it proved to be more work than building the product itself.