Good - As a proffesional You shall never post "job" models (renders if you have permission)
Upload cool looking , interesting models. Showing your shills. Just model anything - mouse, pen, furniture, bike parts.. just pick some.
Imagine what customer you want to work with... Attract him.
Just prove why someone shall hire you and not another foreign name person with ordinary screws / bolts/ models from tutorials/ shitty models with bugs in "model" section.
It will take some time to build nice portfolio but it is worth.
Do not look at me as example - my porfolio is crap- but I do not look for freelancing :) and all models are very old.