I have heard that the 3-4 is superior in run defense. I don’t know if that is true or not, but it has been spoken.
It is easier to find a 3-4 outside linebacker than a really good 4-3 DE. That’s pretty well settled.
It all depends on the players and supply vs demand.
If you have the right players, yes a 3-4 defense is generally better against the run due to the 3 DT+ sized D-linemen.
Obviously the NT is huge (think 320+), but the DEs should be in the 290-300+ lbs range too. It is all about having 3 d-linemen capable of occupying 4 or more o-linemen at all times. If that happens, then the 4 LBs should have little problem getting to the ball carrier. But when you have d-linemen getting blown off the ball a few yards, like Dallas had for most of last year, then the D can be ran on very easily.
As far as which is easier to find, 3-4 OLB or 4-3 DE, that really all depends on how many teams are running each of those defenses.
If most of the league is running a 4-3, then finding those DEs that can hold up going against OTs on a down-by-down basis and being a viable passrushing threat throughout the game are not going to be easy to find. But if most of the league is running a 3-4, then the supply of OLBs capable of passrushing, setting the edge, and not be a total liability in coverage will be difficult to find.
JMHO.