We chose Paddle because of their handling of VAT. It was easy to integrate, and the team was very responsive to teething issues. The payment collection dialog looks great and the split testing/optimisation that Paddle does behind the scenes handles things we wouldn't have time to do ourselves.
There are a few niggles with integration (e.g. no test credit cards) and a few features we'd like that don't exist.
We successfully moved from a long, multi-step checkout process to a simple two step process. This resulted in a marked improvement in conversion rate.