If we think about current personnel, I'm not sure if a 3-4 makes any sense. After all, Easley was probably a player suited for a 3-4 DE role, and now his replacement would be Markus Kuhn (backup caliber) or Chris Long (unsuited).
3-4
NT: Knighton, Branch, Kitchen
DE: Brown, Kuhn, Jones, Vellano, Johnson
OLB: Sheard, Ninkovich, McClellin, Grissom, Flowers
ILB: Hightower, Freeny, Bostic
?: Long, Collins
Long is probably stout enough to play some DE, but would make the most sense at OLB, while Collins could conceivably play either ILB or OLB or even function as a sort of roving player in a 3-3-5.
4-3
NT: Knighton, Branch, Kitchen
UT: Brown, Kuhn, Jones, Vellano
DE: Sheard, Ninkovich, Long, Grissom, Flowers, Johnson
OLB: Hightower, Collins
MLB: Freeny, McClellin, Bostic
Given that Sheard, Ninkovich, and Long all make more sense playing with their hands on the ground and Grissom and Flowers were mid-round picks last season and appear to be better suited for a 4-3, the current personnel is better off in a 4-3 unless there's a ton of draft capital expended on 3-4 players this year.