which "works better" is a very subjective question. As far as just bringing predators toward your location, they will both work, many would argue that hand calls will bring more, but many others would argue that the ecaller will bring more toward you. BUT the biggest difference and probably the #1 reason to use ecallers is that it gets the sound away from the hunter, and if done right, will be a significant advantage when it comes time to kill the predator. Of course the ecallers of today have such an array of sounds to choose from, many of which can't be produced with hand calls, which isn't really necassary unless you're hunting coyotes that get called alot with hand calls.
No matter which tool you use to call coyotes, the hunter still has to set up his/her stands properly, or the out come will be the same, a low kill to called ratio.