Basically, who you pick depends on how much you value sample size (time range). You can really have a good argument for any of the top 4 as they all win their own best time range.
Hungrybox is the number one player of 2016, although very slightly. He has the best record for 2016 and since August 2015. This is of course a very small lead, but a lead nonetheless. Winning time range is high.
Leffen is favored by his 100% win rate against the gods over the past 5 months. It's only a sample size of 1 so the time range is actually nothing but GOML, but that 1 is super convincing as he took down all 4 gods in it, and it was pretty recent. Winning time range is very low.
Armada is the opposite. He's the one that's favored when you draw from a large enough sample size, being the easily most dominant player of 2015, and retaining consistency this year too. Winning time range is very high.
Mango wins by momentum. Recency favors him. He's been 2nd all too much this year, but had an amazing (and patriotic) 1st place finish in the pre-EVO national WTFox 2. Winning time range is medium, as he wasn't too hot last year.
I also want to bring up Mew2king. He isn't as favored as the other 4, but, he has recently shown very convincingly that he can beat any of them which definitely isn't something that any other player can say.
v. Armada: 3-0 at Smash Summit 2.
v. Hungrybox: 3-0 at WTFox 2.
v. Mango: A win and a loss at EGLX, as well as Dreamhack.
v. Leffen: 3 set wins out of the last 4.
It's never been so contested before. It's just such a great time to be a Melee fan and I wanted to put that into perspective a bit. It will be a hype weekend.