tbh asking whats the best mech is like askign whats the best flavour of crisps ( smoky bacon) .. everyones going to have different opinions.
bottom firing, side firing, clone or original, telescopic or tubes. ss or brass. nemesis, roller, caravela, chi you, sentnal, eigelei 18b, King, stingray, nzonic, atom, poldiac.. the list s endless.. start with your budget, and then consider do you want bottom or side firing. do you want ss or brass , do you want seperate tubes or a telescopic, do you want 510 only or 510 and ego threading.. etc etc.. work through your requirements and then narrow the field down to 4 or 5 youve seen that fit the bill then ask again listing those 4 or 5