Here's a link to the summaries of the mainstream methods. They're all capable of being extremely fast, so just pick the one that is the most fun to you.
You CAN get sub-25 with beginners method. I avged like 28 or 29 at iowa, and got a 21.xx single (unofficial). I have recently switched to Fridrich, and my times have gone up (for now).
I recommend any method really. Try a bunch out and see which one you like best/comes naturally to you.
There's no such thing as "the best method" whatever you're comfortable with. Just depends on how hard you work on that certain method. But start off with the beginner's method. and branch off from there.