What is a best and most efficient way to start playing piano? Suzuki method or Traditional? I'm 21 years old.
(I'm assuming you want to learn classical piano, not popular) Since you're already 21 years old I would not recommend the Suzuki method. I don't know it very well but from what I know it's aimed at children.
The Suzuki method is very slow, it relies on the same ability a child uses for learning his native tongue, it relies on a lot of recordings (which may influence the musician towards a fixed style).
Using the pieces selected for the Suzuki method books to study though, can be very good.
It can be a influence from my musical education, but I would go for the traditional method. The most important thing is to find a teacher who can connect with you. I started to study the piano when I was 19 years old, I talked with a lot of teachers until I found the one who had the best connection with me.
Do not go for those online piano teaching courses, it's terrible, those courses will teach you how to hit some keys, not how to play beautiful music. Music is about passion, is about feeling it, understanding it. Only a good teacher, who can connect with you, can pass this passion and this knowledge to you.
Another very important thing is to get a proper piano (or digital piano) as soon as you find out that you want to keep studying. Do not buy something expensive to start of, you may not like it, but be prepared to buy it as soon as you feel that music is your thing, cheap keyboards can be amazing for popular musicians, but you'll need the control a proper piano gives you to keep a steady progress.
A last tip, don't be afraid of theory. It can be tedious in the beginning, but after getting the hang of it, it will allow you to start experimenting, improvising and exploring your piano. This is a very important skill that many strictly classical students do not have, simply because they never tried.
Well, those were the steps I followed when I started and they proved to be very useful to me.
I have been teaching for 50 years. I agree that the important thing about finding a good teacher, once you know he/she is qualified, is to find that connection. Do they understand your purpose for wanting to learn piano? I do not like the Suzuki method for any age. The music books at the level 2 and above are pretty good, but I prefer a graded level for folk, classical, rock and hymns. I ask each student what they would like to play if they could play anything in the world. This gives me a good idea of where their interests are. The emphasis is intervals, expression, enjoyment, popular, standards, and sight reading.