I just switch over to the Simmons TreeSharks. I haven't shot anything but a target with them, so I can't comment on the blood trails. What I can comment on is how they fly, and that is amazing! I was shocked that a BH so big could fly so well. Hopefully I'll be able to tell you how they work on a turkey this spring.    

2 blade heads are pretty simple.  I can't imagine shooting enough stuff to actually see a measurable difference between straight, concave, or convex.  Any tough 2 blade with a decent angle will yield predictable results.  Overall width can effect hole size and penetration, but I don't see the curve, or lack of, along the edge mattering.

Simmons, concave!

Concave.  Howard Hill shot concave.  Is that the reason I shoot concave---Probably

The STOS heads fly real good out of my setup.  They are straight edged.

Straight. Stos. Easy to sharpen. I sharpen them along with my knives using the same stone and same method of sharpening.

I also prefer straight, the tuffheads are awesome.  Single bevel after reading up on Mr. Ashby.  Love his research.  If you get a chance and already haven't read his work it's awesome.

my zwickies start out straight then after a few years of sharpening become concave  LOL

Straight much better for sharpening.  Like the look of a convex and concave head though.

Kris

I have used straight blade heads for the past 20 plus years.  Last year I switched to concave heads for the first time.  I was able to shoot a good handful of critters and can honestly say I saw a lot more blood hit the ground than I am used to with similar straight blade hits.  Pentration was also wonderful.   This year I will be shootin the simmons tigershark again. The great thing about the concave heads are the increase in width you can shoot while still having a great flying head.

I have always shot 3 blade, but killed three deer this year with Simmons, 1 landshark and 2 with tiger shark and I am really impressed.  
ALDO

I'll shoot any good 2 blade i can get scary sharp.But i have been shooting simmons interceptors the last 3 years.

another vote for the Ace standard. Slighty rounded. Very inexpensive, sturdy and easy to get sharp. I have seen some wicked holes made by Simmons heads but they take more efffort to sharpen and cost twice a lot more