Just as clarification, 'hard-easy' is completely subjective, and I don't think anyone is 'wrong' in that sense, I was just commenting on the engine types as far as that goes. The G-2 and G-6 both have the same exact DB-605A engine, and there's not any room for discussion there.
The G-6 probably has the 'worst' combination of characteristics of any 109, and due to being the 'jack of all trades' and not shining in one particular area it may be the hardest to score/land kills in, but its balance also lends itself to flyability in my longstanding opinion. Of course disagreeing with this is totally valid.