How will the crossover slope of 18dB vs 12dB differ in sound, performance, imaging.. etc for sub? is one better than the other? (i have two options 18dB @ 60Hz and 70Hz at 12dB) along with the sub there will be mid/high amp crossed at 100Hz @ 12db slope.
I think 18db slope will give you a tighter bassline and better sound quality bass then 12db slope which will sound looser and not hit as tight. I have mine set at 18db slope at 80hz for my subs and i have my speakers at 12db slope at 100hz and it has a good blend.
18dB is a steeper cutoff, and at 60Hz, a lower frequency cutoff as well. that'll yield a tighter, more defined response from the sub, preventing any midbass from being produced by the sub like you'd get with a shallower slope at a higher frequency.
try both and see what you think of the differences.