I'm working on outfitting and upgrading my Aero Precision M5E1.  It's already setup for the optic and mount.  Next purchase will be either a Magpul PRS or a comparably priced Bi-Pod.

Right now it has the factory installed M4 style stock on it.  Not the greatest for precision shooting, but light.  I do not have any type of bi-pod on it.

So which do you think would add the most utility and usefulness to my build?

Okay what's your goals a range queen I'd go with the prs sand bag it and then worry about the bipod.

If I was looking at actual use in the field I'd go with as good a bipod as I could afford. Or maybe a Harris tall and one of the heavy duty other brands for prone and bench work. Then I'd check out the adjustable luth-AR.
I use my stoney point bipod the most. You will have far more hunting opportunity's standing and sitting. Just food for thought.

I've been around long enough I shouldn't have forgotten to point out my intended application.

It will be used for hunting and target shooting.  The place I have access to has realistic range distances out much further than I can shoot, almost 3/4 of a mile.  

If I were to go with a higher priced bi-pod it would likely be the Atlas which is priced around $220 on DSG arms.  I believe it is their base model.  

I'll look into the Luth-AR stocks as well.  Thank you for the heads up on those.

I'd vote Bipod as well.

I've had decent results using bags on CTR stocks, so those stocks are able to be used for precision.