Personally, I use the vocal workout in Anne Peckham's "The Contemporary Singer: Elements of Vocal Technique".I started with this method, and in a few weeks I had people coming up and asking what the hell happened to my voice. Never practiced before, just sang.
Now, many methods later, I can relate to those saying that it is not the method, but the systematically hours put into it that counts.
That said: It's also important to be ware of what you want with your singing. For me, being a cover artist, copying other artists was very useful in creating the different techniques I needed to be able to deliver variety in my show. Cover artists that sing in a very limited range with one style and one sound/tessitura/voice tends to be very boring to listen to. AC/DC and Johnny Cash It is supposed to sound different.
I would also recommend copying other singers if you want to have a few techniues to choose from. Try saying that a guitar player don't learn other guitarists techniques, it would be insane and don't make sense!