Which one is better, piston 2.0 or piston 3.0? My friend recommend me to buy the piston 2, but I prefer to buy the new one.
Just go whichever you want.
Want Slightly better sound quality? Better mic? Less v-shaped? Want more comfort? Go with piston 3.
Prefer Fullmetal design? Want more isolation? More v Shaped? More bass? Prefer control in the middle? Go with piston 2. You may even get better deal since many shops are having clearance sale on piston 2.
Just saying that if you prefer piston 2, you aren't alone. If you prefer piston 3, you aren't alone too. Both are really great imo. But I still prefer piston 2.