For simplicity's sake, let's just assume we're talking about double-jointed dolls here. How do you like your extremities' joints? Some companies just have a solid seam at the elbow and knee, making it so when your doll's limbs are bent, there's a usually thin piece of resin between the piece of arm/leg. Other companies like to have the elbow and knee itself be a part of the double joint, so when you bend the limbs, you have a bump. Others like to have their knees and elbows be solid all the way around, so you have a sort of stripe going along the joint. What is your preference? Personally, I think I'd prefer the elbow/knee to be a solid part of the joint, but taper around the joint, but not where the back of the elbow/knee is molded into the joint itself.
I think i prefer the tapered block, especially for knees, i think it mimics the appearance of the patella instead of having a straight across seam. But overall i dont really care so long as the elbow peanuts arent squared off- square elbow peanuts really dont have the same natural range of motion as rounded ones and it gets frustrating.
I prefer the knee cap/elbow to be sculpted out and the parting cuts of the joint to be smoothly tapered, so the middle piece is visible when the limb is straight and the edges still flow harmoniously when bent. I started out with a Resinsoul doll and fell in love with the clean silhouette of their elbows, even if they lack a mechanism to hold poses with the joint. (I always wired them anyway.) Sharp edges on a hastily cut joint or weird protrusions coming off a fully bent elbow are distracting to me. They make me think robot rather than organic being and have become a dealbreaker going forward.
Blueblood Doll has the prettiest double joints I've ever owned and functional too. They have a sortof cap or sheath between the top and bottom and when the joint is bent, is covers the slots/holes in the limb so it's just one smooth bend. I think of it kind of like an armadillo curling up.
I love the stripe-looking joint! I think it's so beautiful and dreamy, and just so classic! I don't think I'd want a doll that didn't hav stripe joints
I prefer the elbows and knees to be separate pieces, so the elbow/knee joint is separate from the upper and lower limb pieces and is clearly visible when the limb is both bent and unbent. Since elbows and knees on real people are more like a weird lump than a slit, I think it looks more realistic to have the joints visible rather than trying to hide them and ending up with one gaping split when the limb is bent.
I like the knee and elbow joint to be separate from the upper and lower parts of the leg/arm. It doesn't even need to be even sculpted, it can look bit techy or unsophisticated. I don't really need the joints to be hidden, right on contrary. I think dolls with visible joints look more natural. When one is drawing the human body and want it to look natural and solid, the easier way to achieve it is to exaggerate or enlarge joints. Limbs without this look just like bent tubes, very formless. My preference is a good range of movement over the prettiness of joints.