For the last few months ever since undressai removed nudity, I've been trying several of them, and I have it down to two main ones that I use. Full disclosure, the link that I provide is my referral link, so I will get credits if you sign up. I would appreciate it if that was used, but I totally understand if you don't. :)
The first is
. This one is my favorite.
Image quality is OK. I'd give it like 7/10. There are good customization options. The UI is a bit clunky, like 5/10, but once you get used to it it does it easier. However, this is by far the best one because of how generous the credit system works. When you sign up you have 25 credits, and every day you get 10 credits. The credits do not stack (they used to), so you want to make sure you use them all before getting the next day's credits. But 10 images per day is really solid.
This site has very strong detection for multiple accounts, so I don't recommend trying to game the system with multiple logins and browsers. I got burned by that a few times.
This site also has a feature that I haven't seen elsewhere, which is the ability to swap faces into a video clip. The price is higher (3-4 credits instead of 1 credit for an image), but the results are amazing.
The second is
.
This one has the best quality, easily 10/10. It also has a really good interface, like 9/10. However, you're limited to 1 per day, which is very restrictive. I only use this when something on bodyswap doesn't come out good enough or if it's a really good source image.
You can cheat a bit and use multiple accounts and multiple browsers, so it's really like 3 per day, but that's still really low.