Wac-o-Worm vs Senko
1) Weight allows for nice long casts without extra weight 2) Fall rate is fast enough you can cover water, but still slow enough to trigger strikes from wary biters. 3) the plastic formulation is soft enough that you get a lot of motion of bait.
If you fish them wacky style, the last point is important, less so if you are fishing them texas style. Everything I have ever tried is either too light in weight and I lose a lot of casting distance, or they are way too stiff.
When I first started using this lure it was a secret and now every store in America carries them. The fact it has not lost any effectiveness to me means there is no reason to ever change away from the Senko.
Seems like they are a little less expensive and hold up a little longer than other brands.