Is the use of plastic contrary to the idea of sustainability entirely? Yes.
The general answer to this question is: Avoid plastics whereever you can. Plastic takes several hundred years to rot, it's a first class environmental toxic regarding the high amounts ending up in the nature.
Although, plastic can be recycled in some ways most of it is simply burned or somehow ends up in the oceans. For further lecture on this topic, you should really watch the movie Plastic Planet --- very impressing and should answer most of your concerns. Anyone who is interested in this topic should see this, by the way.
Are some plastics more sustainable than others? Yes.
Anyway, there are some plastics more sustainable than others. They are called organic plastics or bioplastics.
Bioplastics are made from renewable sources and emit less greenhouse gases during production than plastics created from fossil sources. Some bioplastics are even designed to biodegrade within a few weeks.
In the end, it depends on what you want to create in your DIY projects. I would dismiss all kinds of plastics because there are also health concerns.