I have used several of the PayPal type of modules and I actually created a small eComm module using XMod and PayPal years ago. These work well for small implementations.

For larger sites, I have used Ali Commerce and ASPDotNetStorefront for DNN (ML/DNN). Ali Commerce takes a little work to get things setup but for the cost it is pretty functional. Support is pretty good, at least it has been for me. What I learned in the Ali Commerce setup actually helped me during the ML/DNN setup. I guess a lot of it is just understanding basic eComm site setup for Categories and Products, shipping, taxes, etc.

ML/DNN has been a very long journey (18+ months) for me, but it is very feature rich and scalable. They have provided me with a lot of support, but it has almost exclusively been to fix bugs introduced by updates. And there is still a major issue with how they do registration within DNN. If you skip the registration option and only take PP and Google Checkout then then that is not an option. But for me the majority (70%+) of my orders are secure checkout on my site by credit card. And secure checkout requires a registration (kind of), so I still need an update for registration to work the way I need it to.

Here is my ML/DNN site. www.uncommongames.com. Here is my client's Ali Commerce site. www.raiderhaters.net. Feel free to buy some stuff.