Match the adhesive to the plastic
Cyanoacrylate, plain superglue, bonds PLA, ABS, ASA and the composite variants of each without ceremony. It is fast, it is strong in shear, and it is brittle under impact. For most brackets, figures and repairs it is the right answer.
PETG is a poorer host. It has a smoother, lower-energy surface than PLA and cyanoacrylate can sit on it rather than grip. Keying the faces with sandpaper first makes more difference on PETG than on anything else, and epoxy is the more reliable choice when the joint matters.
TPU and the flexibles need an adhesive that stays flexible. A rigid bond on a part designed to bend simply moves the failure to the edge of the glue line, and it will fail there on the first flex.
Epoxy where the joint has a job to do
Two-part epoxy is slower and messier and it is what you want when the joint is structural, when the faces do not meet perfectly, or when you need working time to align parts. It fills gaps that cyanoacrylate cannot bridge, and it stays tougher under impact.
Printed faces are rarely as flat as they look, particularly on a face that was against supports. Epoxy is forgiving of that in a way a thin adhesive is not.
Solvent welding is a different thing entirely
Acetone dissolves ABS and ASA. Applied to two mating faces it softens both, and as it evaporates the plastic re-forms as one piece. That is a weld, not a bond, and it is stronger than any adhesive joint you will make in those materials.
It only works on plastics the solvent attacks. PLA, PETG and the nylons do not solvent weld with acetone, and attempting it produces a wet part and nothing else. Do not extrapolate the technique across materials.
Acetone is flammable and its vapour needs ventilation. This is a job for open air or an extracted space, not a closed room.
Prepare the faces, and design the joint
Key both faces with sandpaper and clean off the dust. A printed surface looks rough but its ridges run in one direction, and adhesive keys far better into a randomly scratched face than into parallel layer lines.
Where you control the model, give the joint some help: a lip, a peg, a recess, anything that locates the parts and adds bonded area. Adhesive is much better in shear than in peel, and a flat butt joint between two printed faces is the weakest arrangement available.
