When asked this question most people will say either 2 or 4, but i think 5. Let me explain why. When 5 came out it was a huge deal, everyone wanted it after the success of 4 and capcom came out of the gates confident with this one. They came out with a big exploding action game that was accesible to everyone including people that maybe hadnt been interested in the series before. 5 also felt like the apex in terms of story as they closed a lot of the storylines ( the last two big bad guys left, spencer and wesker were killed) and it looked like chris had successfully finished the last of umbrella. In short, in my opinion 5 was the last RE game that capcom seemed really confident with, every game since then like the first revelations has almost felt like capcom are saying " hey we still got it right?". Me personally il always play RE whatever capcom do with it but yea, in my opinion 5 was the last game where capcom were really sure with what they were doing, they were making a big fat action game. Now before anyone jumps down my throat i know 5 isnt extremely popular, and there are qualitys about 2 and 4 that are better than 5, but all im saying is this felt like the last confident game in my opinion.