No.
There are several areas where the UI simply isn't up to speed compared to iOS 7.1.2.
The main one first and foremost is the keyboard delay. I had my iPad Air on iOS 8.1 replaced at the Genius Bar by citing slow WiFi issues (which I had, another wonderful side effect of iOS 8).
My replacement is on iOS 7.1.2 and there is no way I am updating. Typing this message now on my iPad Air the keyboard is a joy to use, every key is responsive, there's no delay or feeling like the letters on screen struggle to keep up with the speed I press the keys. On iOS 8.1 there was.
The UI is a little slower, the five finger pinch to home animation has a slight delay which gives the feeling of the device being slower. The animation when the apps return to the home screen when using the five finger pinch gesture can sometimes stutter at the last part of the animation.
On Safari when you are on a website and tap the current address in the address bar, there is noticeable lag in the animations where the address highlights grey and slides left to reveal the entire address (keyboard and favourites box come on screen at same time). The same thing is super smooth on iOS 7.1.2 although there's no big translucent favourites box (on iOS 7 the entire background goes semi transparent white with favourites rather than drop down a big box like in iOS 8).
There are simply lots of little UI quirks in iOS 8 which make the iPad Air that little bit less enjoyable to use compared to iOS 7.1.2.
Again, some people won't notice these things and see iOS 8's performance on iPad Air as acceptable. That's fine, but these issues exist and I wish I couldn't notice dropped frames and stutter with the naked eye, but alas I do.
Keep it on iOS 7.1.2, unless you want the Metal API for games (for the record VainGlory and Asphalt 8, the two biggest Metal titles thus far, run and look fantastic on iPad Air with iOS 7.1.2 anyway), want to use interactive notification for iMessage, or enable cross OS X/iOS notifications/handoff features then there's no reason to upgrade to iOS 8 on iPad anyway.