It's tricky because he is such an x-factor player that you want him in your team but the shot that he played today makes you pull your hair. If nothing works out, I would even open with him but that would push Rahul down the order. So it is difficult to figure out what is the best position for him.
His best position is at either three (where he plays for the Stars) or at four (where he plays for Australia and has two centuries). Maxwell works best when he gets to play his brand of cricket where he starts off steadily with good rotation of the strike and putting away the bad balls for boundaries, preferably before the powerplay ends. It is when the situation demands him to be aggressive right from the start (or is told to do so) or the game is in a state where you can afford complacency that he starts losing his way and plays those funky shots. The only other time they appear is when he is well settled and seeing the white ball like a beach ball.
His strike-rate has most people fooled with the style of cricketer he is when in reality he is a less consistent version of AbD or any other highly aggressive top order batsman. At the death he is going to struggle if he comes in fresh barring the odd game where he just goes berserk and lady luck favours him. And no, he is not inconsistent for a top four role in general as I've seen numerous smart performances from him for the Stars and in Australian colours.
Now the big question is if Maxwell the IPL cricketer deserves a top four role given how poor he has been in most seasons barring 2014 in this same country for the same franchise. Which is why I think if you're not going to play him in his preferred role, you might as well go with Neesham who is a gun cricketer himself solving the issue of a middle order hitter and a supporting death bowler for Jordan, both of which his team needs (Maxi bowls off-spin too which is already covered by Gowtham). He also has a very good fighting mentality which is something that this Punjab side could definitely use as shown today. I do not think he would have ever played that brainless shot that Pooran did for example.