The right filament depends less on which is “best” and more on three questions: what temperature will the part see, will it flex or take impact, and how forgiving is your printer?
PLA — the default
Cheap, easy to print, low odor, low warping, and surprisingly stiff. Softens above 55 °C, so don’t leave parts in a hot car.
PETG — the functional generalist
Tougher than PLA, better moisture and chemical resistance, easier to print than ABS. The default choice for functional parts that don’t see high heat.
ABS — when heat matters
Best heat resistance of the three (≈100 °C glass transition), but needs an enclosure, prints with strong fumes, and warps aggressively without one.
Quick decision rule
Indoor display or model → PLA. Functional part that stays under 70 °C → PETG. Hot car, engine bay, or sterilization → ABS or beyond (PC, ASA).