I don't have Swype, but I use Slide It everyday. I love it. Much more fun to use than Swift Key and normal keyboard. I find it to be quite accurate when you focus on getting most of the letters in your words. It has good word prediction. I'm using it right now to do this reply. I do make mistakes, especially on long words or words that have multiple same letters. For example, a word like "especially" may be difficult because on normal typing, you would type two "l's" but with Slide It, you only swipe one "l". Sometimes with long or less often used words, the prediction doesn't give you the word. I've found that if you go slowly & concentrate on getting most of the letters in, it will be quite accurate & pick it up. The keyboard does have a typing feature, which is ideal for names or other words you may want to add the dictionary. Also you can type while in Swipe mode to make quick corrections. I find this keyboard a lot of fun to use. I find the highly recommended Swift Key to a lot less fun to use. Once you get used to swiping, you won't want to go back to typing... Well, at least for me! I don't have Swype, but with Slide It, I don't find myself wishing I had Swype. This is a fun keyboard once you get used to swiping instead if typing, but you can type, too, when you need to.
I prefer FlexT9 personally. No-one gives it props for some reason, but I love it. It has word prediction, Swype-like entry, Dragon voice entry, and trace entry, though I never use that functionality. No skins, but that's not a big deal to me.
I personally love Swype. I haven't tried SlideIt myself but I've had Swype ever since it came out and it's just became an amazing keyboard. I'm not sure what extras SlideIt has but I'd definately recommend looking at Swype's "Tips". So many useful and clever techniques to help you utilize Swype even more