What is the best Rom for performance and smoothness ?

My phone feels laggy and slow, even if i do a factory reset the phone is not really fast anymore. I am all about power, speed, smoothness. I dont care about many features.
Btw i am a total noob i have no idea about anyhing
Will probably check some YouTube Videos about rooting and flashing roms
Maybe there is something important i should know before i Start
If so let me know :)