If you want to upgrade to iOS 8 and jailbreak with the PanGu jailbreak tool, do so now. Apple has released iOS 8.1.1 and it "breaks" the tool (there is no jailbreak on iOS 8.1.1). Once Apple stops signing iOS 8.1, the only iOS you will be able to go to is iOS 8.1.1.
Right now, the jailbreak on iOS 8.1 works fine, both on the iPhone and the iPad. There are still tweaks that have not been updated for iOS 8, but developers are hard at work getting stuff updated.
I am successfully using iOS 8.1 on both my iPad and iPhone. I've had no issues and they both work fine.
No one knows when Apple will stop signing iOS 8.1. So, if you want to go to iOS 8 and jailbreak, best to go while the getting's good. Else, you'll be "stuck" at iOS 7 with a jailbreak or on iOS 8.1.1 with none.
No pressure ... but you've really got no time to make a decision.
Marilyn