I think there's a little more to it than that...The 360 is a truck motor. The 340 was never anything but a quasi-race motor...never had a two barrel, always had a double roller chain, ect. The T/A was based on the 340. The X blocks were based on the 340, and that was back when the 360 was taking over. The R blocks, were based on the 340, and they turned into the whole R-family. The 360 evolved and took over the position of production, performance, small block, but the 340 evolved and turned into THE full out race motor. The 340 enjoys that celebrity regardless of how a 360 performs.
If this decision were mine, I would build the 360. Fortunately I have 340s. (I just took the T/A 340 out of my Demon and sold it to the E-body crowd.) The 360 has taken over the aftermarket, and that is enough of an excuse for me to go 360. Cheap parts. However if I were building a stick car...I'd put a forged crank in it.