Depends on the campaign. . .
As Saba, I use mostly regionals with a few Saba native units to remind my enemy who I am.
As Getai, the only regionals I use are the elites (Kluddos Lugos, Cardinau Orca), with everything else trekking in from the homeland. The exception are my raid armies, who tend to be almost exclusively mercenaries.
I haven't got very far in my Luso campaign, but I like their factional units, so it will likely mirror my Getai campaign.
My Baktria campaign is RP'd as a breakaway Indian faction, so I'm using the Indian regionals as my faction troops. . .
I haven't got far enough in my Roman or Ptolie campaigns to decide yet, although I do HATE phalanxes, so if I continue the Ptolie one for any duration, I'll likely use lots of regionals.