Been a longtime RK/Hydrodynamica devotee.
Golden Mean Machine: I have the second iteration (channels in the tail) and it's literally a Swiss Army Knife. The true daily driver of my quiver, never worried about wave size with this puppy it will handle it all. I can put any set of fins (twin, tri, quad) in and while the ride will change the board just goes.
Cyber Sim: Simmons/Tomo hi performance mashup. I felt it was the heir to the Tomo Nano, hi performance but more paddle power.
Simster: Mush machine, I got a Bauguess when he split from RK. It was magic, such a fun board in waves up to shoulder high, above that it went too fast. This board kicked off my fascination with grovellers and it's one board I wish I never sold.
Casper/Mini Simmons: I was lent one of the originals and it was a trip to ride. It was big, fast and the half moon keels could turn surprisingly well. It was unpredictable though, one second you'd be in total control, but if the next section would have any steepness it would just squirt out from beneath your feet. RK is a wizard to make the original Casper look so good.
White Pony: The first Hydrodynamica shape I purchased, it was from Mabile. I couldn't stomach the $1,000 board price from Hydrodynamica and Larmo was quietly (but approvingly) making White Pony's under his label. The Pony is a bit more refined than the original Mini Simmons, more predictable and closer to the ride you'd get on Larmo's keels. Larmo recommended I get it with standard keels but I was set on the half moons.
All these shapes had a common sizing recommendation that Tomo made to me when I ordered my first board: "Chin height."