I say the Assassin's. I've gotten so many compliments on how mine sound it's going to be hard (but not that hard) to get rid of them for my Fi Q >_>
i have yet to hear the ssi 8", but i wasnt impressed at all with the 10"ers, they are so power hungry that it isnt really worth it. a tsx 8" would be badass. but i would have to go with the DD 8" if i were looking at 8" woofers. i think my next install is going to be either one DD 12" ported, two lower series ported, or maybe three or four 8"s ported. havent really decided yet.