I've used Swype for a long time and Swiftkey/Google keyboard (swipe version) about equally, well a little less on Swiftkey.
Keep in mind, comparing these keyboards swipe ability with tapping ability will get you nowhere.
For swiping exclusively:
Swype: Much less aggressive with prediction, but it's much easier to type specifically what you want or complex things that aren't easily predicted.
Swipe/Google: Much more aggressive prediction, including auto-spacing, but it can be kind of annoying to string together customer words.
Example:
In Swype, it's a lot easier to type Mincraft by swiping 'Mine' followed by 'craft'. Swiftkey and Google will add a space when swiping two words.
Typing a normal paragraph quickly in Google/Swiftkey will be much easier/faster.
This is just from my experience. I would really like to try Swiftkey/Google with a feature that disables the auto-space in between words.