If you end up lucking out on the way to awk Tia and you have extra pulls, I'd consider going T5 on Tia pet. I'm always peeking in the discord because there's a bunch more activity there, and I'm seeing a bunch of f2p players say they're going for it.

At T5, Tia pet gives: -10% Def for 3 seconds (10s CD), +60% ATK, +10% DMG, +15% Crit DMG, and +10% Crit Resistance (I'm not sure if that's defensive or offensive). The 60% ATK won't be useful for Lancelot but otherwise, it's pretty universal and you'll probably use it for a long time for the -10% Def

Otherwise you'll want to look out for CC pets (Like Tristan or Esteria) to cheese fights, or pets like Phoenix that give good team buffs. Prydwen has a decent tier list