Rengar is the most fun mechanically (also kills), but he's gonna get reworked. He's a weak laner, supposedly, but good late, weak jungler too supposedly but I have had mostly fun with him, his ganks are amazing and he's a tricky fighter in the jungle. Also cracking towers really fast is always valuable in solo Q. But yeah. Rework. S4 seems to have less bush on map too, so IDK how Rengar survives that.
Khazix on the other hand is entirely based on kill stealing so you can run away more. When he was good he was bullshit, now he's mostly annoying to his team the same way AP Yi used to be. Maybe he's really high skill cap or something, I don't know, didn't you already have Zed, I bet you're going to be disappointed on the Zerg after the Shredder.
Hecarim needs a lot of gold to do dick, so you take kills and farm from your teammates, of course when he has gold he does horse dick. In other words he's good if you're an asshole jungler like me. Giving kills to ADC? Yeah my Nocturne assassination build isn't going to buy itself so suck it, yeah you go on ahead shooting towers that don't fight back while the real men go about the killing business.
Brand is pretty damn good in my opinion, you can build Rylais and Liandrys, use one spell and watch their health burn away, also they're slowed forever. Or you can just build pure AP and watch things go boom. He can bully lane, farm safely, win teamfights, roam adequately, duel, 100-0, he has a lot of good stuff, but no mobility or utility. He's not like for example Lux who is always safe due to massive range, CC and op shield, nor like Cassiopeia who has this complicated kiting pattern and DPS, Brand is pretty much AOE murder burst in a blink of an eye and that's it. What I like most about him is that he has great ranges and cast times so you almost always get to cast everything.
LB has an interesting playstyle but I feel like they've gutted her damage at some point, she's not like Jizz who just 100-0's you on reflex. Her spells are interesting, but she's not a lane bully anymore and I actually think she has a pretty difficult laning phase now.
I just found out something odd, Skarner with Triforce, Gunblade and sunfire apparently can duel and kill a fed ass full build Darius, this just happened on TT. Like what the hell? Full healths, possibly I had ignite and he didn't but C'mon. I had forgot how fun Skarner is when you're at the point when he completely stops dying to anything.