I think its always a good idea if you use your own models rather than tutorial models for your portfolio because it shows your own imagination to an extent.

But if your like me and have lots of tutorial pieces I think its fine to start off with. Maybe you can modify them to make your own. For example if done the ferrari tutorial from this site but i've add an interior, different alloys and some decals to make it look a bit different.

It would be good to hear what people in the industry think