I'm not sold that a 3-4 or a 4-3 is inherently better, but I will say that I think it is a lot easier to find LBs and DE/DT's to play in a 3-4 than a 4-3. For whatever reason, there do not seem to be a lot of 4-3 LB's that can play the middle or strong side coming out of college, but there seem to be a lot of those tweener guys who can play OLB in the 3-4. Also, there seem to be more guys that can play MLB in the 3-4 than guys who have the combination of size and speed to play MLB in the 3-4. And, although Vilma was not happy in a 3-4, he is older and slower now and we could still use him as a nickle and dime LB while letting him rest or have less field to cover in the based 3-4.
In the end, I think it's time to more or less start over in the front 7 and it would be faster to re-build to a 3-4 through the draft rather than to try to build a 4-3. There just seems to be more 3-4 talent coming out of college. Look at what the Texans did in one draft.