What are the advantages of Jungling as Kha'zix vs. Rengar?

If you don't feel like reading all of the stats below, Rengar is better for team fighter, and Kha'zix is better fit for team play, as he's reliant on his team. All in all, Rengar is the better jungler, and more steady, efficient, and quicker at clearing.

Rengar is best in the new jungle mainly because there isn't much early aggression so you can farm to 6 and gank wil ult. The only problem is that Rengar takes good decision making and good management of your Ferocity stacks(which is hard because the camps are harmful). Overall Rengar is more impact and carries so hard if you play him right.

Kha'Zix is basically following up on your team, although he has much more damage and a more balanced build, but his lower health makes it risky to clear, while Regar is more self-reliant and capable of clearing.

Kha'zix's Lvl 1-18 statistics are the following:

Statistics:

HEALTH 573 – 2018 ATTACK DAMAGE 55 – 108 HEALTH REGEN. 7.5 – 20.3 ATTACK SPEED [*] 0.668 (+0% – 45.9%) MANA 327 – 1007 ARMOR 27.0 – 78.0 MANA REGEN. 7.6 – 16.1 MAGIC RES. 32.1 – 53.4 MELEE 125 MOV. SPEED 350

Rengar's statistics Lvl 1-18 are the following:

HEALTH 586 – 2116 ATTACK DAMAGE 60 – 111 HEALTH REGEN. 4.3 – 11.1 ATTACK SPEED [*] 0.679 (+0% – 48.5%) FEROCITY 5 ARMOR 25.9 – 85.4 MAGIC RES. 32.1 – 53.4 MELEE 125 MOV. SPEED 345

Check here and here for verification on stats.

Now, we're going to break it down into raw rates and percentages.

Kha'zix has a 52.01% win rate, while Rengar has a 50.9%. Just as Kha has a 11.2% pick rate, while Rengar has a reduced 8.1%. This is mentioned for the sake of popularity. Answering your question as which is a better Jungler, Rengar can build one damage item and go tank and still create plays to one shot an ADC with good decision making. Kha'Zix is team reliant, but if you get some kills you can snowball hard. Pretty squishy though so you can get shut down pretty easily.

The only thing Kha'Zix had going for him was that his W severly increases his sustain compared to Rengar, who can only heal when his ferocity as maxed. However, the recent increase in CD kinda kills it a little bit. Kha may be able to get an extra camp or two early game, and the extra health he gets could result in an earlier gank than you might get from Rengar. I think while the one or two early camps and ganks could set up a little better for Kha, Rengar is still the safer choice.

A full break-down of the comparison of Kha'Zix vs. Rengar can be found here. If you're looking for a second opinion, and a mass opinion on the official League of Legends forum, check here.