Between the 3-4 and 4-3 schemes, they both provide value to certain teams. Among the top 10 defenses in the NFL in terms of points allowed, five teams run a 4-3 defense and five teams run a 3-4 defense. Both defensive formations have their benefits but in the Baltimore Ravens case, they would be better suited to switch to a 4-3 defense.
Earlier this season, I wrote an article saying that the Ravens should go to a 4-3 defense which also discusses how the Ravens already have key players in place to play a 4-3 defense and as the season goes on, it becomes more convincing in my opinion.