I prefer a normal layer. If you practice enough, you'll find normal lineart to look more natural and go much more quickly. Although I do rely on line work for trickier lines, such as a line with several curves. I think using a bit of both makes the most out of sai
I say whatever float your boat. Mostly I would say to use the lineart layer since its supposed to function for that. I know that line art is at its best quality when used in Sai. And also since its vector, its alot smoother then pixels and vector tends to resize better (until you convert to raster layers).
But if its regular like sketchy lines, vector isn't necessary, and its better to use pixel art.
i like the normal layer on s-5 or above, mostly because i can easily change the color of the lines with the opacity lock. i dont know if i am doing it wrong, but i cant seem to change line art colors with the line layer.
I use the line art layer. I would like to move to regular layer cause it gives more natural lines (which is why I do all my eyes by hand instead) but line art layer is alot easier for me cause I have shaky hands. haha. I would love to transition to reg though.
Line work and Normal are two very different ways of rendering. Line work creates a vector line mean that it can scale infinitely in both directions. This is a double edged sword. What you are gaining in sharpness you are losing in raw rendering. This is why many people prefer to do a rough sketch then do a line work layer on top to get those perfect lines.
The line art layer is vector based. Meaning instead of using pixels it uses a mathematical equation to draw lines, color,ect. That is why you can manipulate line art layers and get 0 pixelation. When you are changing how the line looks you are changing the equation. Now I want you to make a super tiny speck in a normal layer. Then use transform to blow it up super big. You will get lots of pixelation and muddy edges. If you do this same experiment on a line art layer the edges will still be sharp. This is because it's vector based, while a regular layer is pixel based. The second you save it as something like a jpeg it turns it all into pixels.
Again, not in SAI. The line art created in a linework layer on SAI is still being created as a bitmapped line. The guidelines for that line are vectors, sure, but not the actual line itself. Zoom in though, and those lines you're making will get pixelated just like all the rest.
With my shaky hands I use the vector lineart layer for my lines in Paint Tool SAI. It's one of the reasons I got SAI. Others can be confortable with the regular layers for lines if they can used to the constant draw - Control Z, draw - Control Z, draw - Control Z all the time. But then unpredictability of the hand drawn line is something they might want in the first place. I like control over my lines which also means I have to have a solid sketch to reference by.