I like both of them.

I prefer a mixture. Sadly, I can't do the thiner + thicker lines with my mouse. . .So for my own stuff I prefer thinner lines, but on others I prefer a mixture.

Eh, I should have put mixture, but to me, lineart should vary by what "feel" you like to give in your art. Thick lines attract attention to the subject and work better for cartoons. While thinner lines make you focus more on the picture as a whole and the finer details. Oh wow. I gave advice.

I like thin lines for the details and thick lines around them. for example, a handbag with all the stitches and pockets drawn with thin lines but a think outline around the bag itself.
Did that make any sense? xD

I like them all, but I really admire how folks can mix thin and thick lines just right.

I'm a thick lady, so I love thick lines~!
*shot*