if it was still 1975 yes you would want the 340. but thats because no one made pistons (well cheaper off the shelf) for the 360 so the 340 was the budget way to go because at the stock bore you had compression, if it needed to be bored there were off the shelf pistons. these days a 360 will run anywhere you want it to because there are tons of parts out there for them and all kinds of off the shelf pistons.
same deal with the 400. people used to throw 400 out all the time. screw a emissions 400 they would rather have a 383 over a 400. well everyone wants 400s now. why is this? because they make pistons and stroker kits for them now...
me i'll take a roller LA or magnum 360 over a 340 every day of the week and twice on sunday. 340s are great to make cash on to the numbers crowd though.