You really want a 1 that also serves as 2
For example, in the days of Miranda Nym, I had a lot of success running two TIE/D Defenders (One with Ion, one with Flechette) alongside OL, who could tap an opponent and leave it immobile and helpless to a storm of dakka. It surprised everyone else too, and did decently against almost everything that was thrown at it - in its specific example, synergy lists and imperial arc-dodgers tended to cause it problems, but that was about it; everything else it could at least hold its own against.
So really, build something that is particuarly decent against 1 if you suspect to see a lot... but make sure it's able to take on most of what else is out there in the process. Even if it's tweaked towards countering one archetype in particular, being general-purpose as well is, well, what makes something a 'good list'.