they both have a place. ive thought about using A flat blade kn some of the portraits ive done, recently the tiger swallowtail butterfly, but with 500+ cuts thats 500+ times id have to turn the work 360 degrees and many of the cuts are juuuuust about 360, the back the other way, turn here, go up, turnturnturn...i find it much easier to use spirals in that situation.
blade control for me seems to be combined with saw speed and the pressure i apply.
but then theres other portraitwork requiring veining where a spiral is too wide.