'Fair' and 'Unfair' are actually jargon terms. In Netrunner, it's analogous to saying that a deck 'plays Netrunner'. It means what was said before; Fair means that a deck does traditional Netrunner things like Run on Remotes, try and establish a lock on some server, and leverage it to victory, or else build up enough ICE/Upgrades to be able to score out of a Remote. 'Unfair' decks don't Play Netrunner, instead they get 7 points in one turn (CI7 or Dyper) or otherwise 'subvert' the rules of the game to get a win. (Any deck that wins through Power Shutdown, or by getting a whole bunch of clicks in one turn...)
So, that said, 'fair' and 'unfair' have nothing to do with how the player feels playing against them, only what the deck's win strategy is: Traditional Run to Score or Glacier (some, including me, count Fast Advance in Traditional Netrunner.)
The only unfair runner decks right now are En Passant Val and Dyper. The strongest Fair deck is either Power Tap Andy or Temujin Whizz.
There's a bunch more unfair Corp decks right now, because it's way easier to do an unfair deck on the Corp side, since Runners aren't guaranteed 7 points even if they can get into every server ever. You have Yellow Railgun decks, that use Power Shutdown + BOOM! to kill, CI7 obviously, and you can make an argument that IG49 is 'unfair' by this definition... For the most part, Corp decks are more likely to be Unfair because Runners are more likely to be able to deal with Fair Corps. The strongest Fair Corp is CtM, as it requires a bunch of tech to bring the matchup to almost even, and then you have Blue Sun, HB decks (AoT and ETF are... roughly similar.), and the PE that always exists on the sidelines.