Not in favor of 3-4. Harder to find players for it. Also Jerry has been in love with Seattle's 4-3 for the better part of a decade.
"Harder to find players for it" all goes in cycles.
It is really hard to find that true 4-3 passrushing DE that is also a good run defender. It makes it even harder to find those guys when over half the league is playing in a 4-3.
Just like it is really hard to find that 3-4 OLB that can pashrush, hold the edge and not be a complete dunce in coverage. Again, even harder when half the league is playing in a 3-4.
Dallas originally move to a 3-4 Defense is because they tried and failed over and over again at finding good passrushing DEs while using high draft picks with guys like Ebenezer Ekuban, Kavika Pittman, Shante Carver and even, to some extent, Greg Ellis. The first 3 were garbage and Ellis was never an "elite" passrusher. A darn good player, yes. An elite passrusher, no. BTW, Ellis' best passrushing season, by far, was when he played as a 3-4 OLB.
Then Dallas really had to move back to the 4-3 due to missing on Bobby Carpenter and Anthony Spencer. And none of their later draft picks, Erik Walden, Victor Butler, Brandon William or Kyle Wilber was able to step up either. Then to top it all off, they refused to find a TRUE NT to anchor the middle of the D, instead opting for the "1-Gap 3-4", which to me is an oxymoron.
Either way, it is hard to find those great cornerstone pieces of ANY defense, but it can become even harder when fighting with most of the league for the same types of players.