In terms of taking cards (not paypal, stick with them, the more options a customer has the more chance of a conversion):
I spoke to paddle this week and another plus for paddle here in the UK is that they transfer funds to UK banks with no fees.
I've also been looking at stripe. If you are using paypal already and just need card payment then they might be the way to go.
I integrated countless customers back when I was doing web 15+ years ago through many payment processors, some of which have since closed or been bought out by worldpay. With worldpay, getting a merchant account will be your biggest hurdle from there integration will be similar to stripe, but again you will get a marginally better % rate with worldpay but you need to go through more work, PCI compliance etc.
It basically boils down to time vs cost.
Time to implement vs cost in % for the service.
Paddle looks super easy to implement but they take a little more % off the top for the trouble of taking care of the vat stuff (not an issue if you're not worries about vat).
Stripe might take a little longer to implement but you can make it the way you want it and they take a lower %.
Worldpay takes the most time and you get the best %.
What it boils down to is do you take the higher % and peace of mind or involve yourself more and get a better/lower %.
Personally, if you have a low throughput then go with paddle and move to stripe and/or worldpay if you are getting in plenty of sales where it will be worth doing the extra work for that extra 2-4% which might turn into a sizeable chunk of change in the long run.