Following hsbcn: You will have to be much more exact.
The three materials will have differencies in different degrees for at least: corrosion resistance, weather (snow, water, sun) resistance, heat leading and shielding factors, construction strength, fabrication and maintenance cost, shock resistance, vibration damping resistance, radiation resistance, fire and explosion resistance, mechanical wear and abrasion resistance, detoriation over time (plastic and UV light?), weight, mounting/demounting and mounting of extra accessories and equipment, etc. etc.
In addition plastic, aluminium and steel are general descriptions which can vary and overlap in qualifications from material to material depending on exact alloy or plastic type and surface treatment/finish. Actuators type, size and applications can vary in a vast number.
There is no general answer to your question.