For 90% of the people out there it really doesn't matter one bit what the best broadhead actually is. Most people buy what ever broadhead (or any product for that matter) gets the most air time on television, has the most pro hunters promoting it, and has the most print ads in their favorite magazines.
But to answer the question.
I look for a few things in a broadhead.
* I prefer steel construction over aluminum.
* I test the overall durability (ferrule strength, blade durability, blade retention) by shooting things like plywood, cinder blocks, steel drums... not many hold up well here.
* Scary sharp blades.
* Great flight characteristics with minimal tuning required.
* Total cutting ability. (not cutting diameter but total cutting ability)
The broadheads I have found to make the cut in everything I look for in a broadhead are Slick Tricks. I have yet to find a broadhead that puts it all into a single package like the Slick Tricks do.