I'm hoping to hear from someone who has used something other than the cheap stock replacement stuff and found it to be good.
I make my own.
First off let me recommend at least 3/8 diameter for performance work. Especially if you think you may upgrade to a bigger cam at some point in the engine's life. 5/16 pushrods are marginal for any hipo work. Friends of mine who run Comp engines have found out on a Spintron (essentially a dyno for valvetrains) that with their huge cams even a 1/2 inch tapered pushrod in the lengths needed for an inline six is marginal.
I order 3/8 4130 chrome moly seamless tubing in bulk lengths. I ordered the correct ends from Crane. After calculating the correct length I cut the tube to size, reamed the ends and pressed in the ends. The first time I tried to press in the ends the pushrod buckled before the ends seated. So I made a sleeve with a 3/8 ID and used that to enhance the "column buckling threshold" by slipping it over the pushrod before pressing in the ends on a hydraulic press.
There you have it - another speed secret from The Frenchtown Flyer