I would offer this advice as a long-time FL player: avoid fretlines and go with side dots. I say this for two major reasons:
1. Fretlines supply a false sense of proper intonation. The lines just don't tell the story; your ear does. In general, setting the intonation of a fretless bass is different from a fretted bass because it is so dependent upon the string height and the finger positions used to set the correlation between the open string and the octave. You can use the 12the "fret" harmonic, but that has its own set of problems depending upon how you finger the actual note.
2. In most normal playing positions (standing up, I mean), you shouldn't have to struggle to see your fingerboard; this can create neck and back pain. You should be looking at the side of your neck for the fret dots, which, on an unlined fretless will be at the the proper pitch positions. On a lined fretless, the dots are most often at the "mid-fret" positions (like a fretted bass), which forces you to look at your fingerboard to find the line.