Bennies are a bit controversial because, as you said, they can be biased.

However, that is in a way also their greatest strength as a game mechanic. I believe the recent surge in tabletop gaming stems from an entire generation being raised on computer games. We understand the fun of games but also the limitations of computers. Computers can't judge things like a perfectly-timed punchline, an "epic moment," a great piece of roleplaying with another person, etc. Bennies are a mechanic that play directly to the squishy human factor at the table, relying on our ability to sense what makes a particular moment interesting, fun, or memorable. And so, in my opinion, it's a shame when people tie bennies directly to predictable game mechanics. It's surrendering part of the human element of RPing. I know this all sounds high-falutin and kinda pretentious, but if you think about it you might see where I'm coming from. It's similar to how Savage Worlds restricts itself to simple addition and subtraction instead of demanding complex, time-consuming calculations: the system is designed to play to our crappy brains' strengths and downplay our weaknesses.

THAT SAID, I also agree that GM bias is a problem with bennies. I always give more to my wife than anyone else. So, to combat this, what I do is have my players nominate each other--and nominate me--for bennies. If someone pulls off a great moment there's usually a chorus of other players demanding he get a bennie for it. Likewise if I improvise a scene well, or pull an enjoyable character out of my ass, then the players will nominate me. Nominations are really fun and add to the energy at the table.