Please refrain from arguing who is better than who. Each person has their personal preferences.
Personally I like Rahiden http://rahiden.deviantart.com/. He has very interesting complex designs (sometimes overly simplistic), never breaks his color scheme and his MOCs look fun 
.
@Shadowgear6335 is da bomb
I donāt knowā¦ might come back later if I figure outā¦
Yeah, Rahiden is really good.
I also liked his Hero Faffory comic that he made.
Iām a big fan of a lot of the stuff Ids5621 makes, especially his Magneon MOC
Fenrek is another phenomenal MOCer in my opinion too
/s
Seriously, thoughā¦
I would have to say,
Either JANGBRiCKS, DrScorpionX, @CallanLOF, @MrBoltTron, @Ventum, @Ekorak, or @Venom.
Probably one of my favorite mocists would have to be retinence on deviantart.
I remember him 
Although I didnāt watch his videos. I remember he and other popular MOCists collaborated together.
iBionicle, ids5621, Larnuu, TheBoltTron, and King Cyan are just a few I can name at the moment.
I like most of Squeaverkingās MOCs.
I appreciate my brother, @ToaKylerak, and his MOCing skills. He makes the Inika build cool again.
DrScoprionX is cool.
His MOCs truly are amazing :O.
BioTube MOC appreciation is like pop music appreciation. Itās good sometimes but is usually way overrated. Although arguably Shadowgear is starting to live up to his fame.
I define āfavorite BIONICLE MOC buildersā as the ones that I look up whenever I feel like I need inspiration. Those people include Chro, Fenrek, CommanderSpencer, Ventum, and X.
My favorite MOC builder is myself! 
Pretentious man.
I think Iāll just say anyone from the bronze-golden era of biotube
Me
I must say, while he might not agree, @Chro is a nice builder.
@Shadowgear6335, @MrBoltTron, @Chro, @Likus, @Venom, @Ventum and @Ekorak are pretty great mocists