There is no "best" answer to this. That's why there are so many vaied products on the market. If any one could be siad to be the "Best" then there wouldn't be any need of all the others.

However, the best broadhead is one that is scary sharp and aligned properly with the axis of the arrow. Simple as that.

The next thing is the arrow. The best arrow is one that is spined properly for the bow weight and length of the arrow, draw length, etc. It must have sufficient weight to carry enough momentum to achieve penetration to the vitals. The bow/arrow combination must be tuned to shoot the arrow as straight as possible so it's not wobbling around.

Notice I did not say to tune the arrow. You do not tune arrows. You tune the whole setup so it acts as unit. Now, to this end, you can get arrows from manufacturers such as Gold Tip, Easton, Carbon Express, Carbon Tech, Carbon Impact, PSE, and others. It really doesn't matter a whole lot. They are all good; some better than others and priced accordingly. All you need concern yourself with is getting one that is spined properly. And if you are shooting anything over 50# any properly spined arrow will be sufficient for deer.