Good threads are strong, have long fibres, and are relatively smooth; bad ones have short fibres and are fuzzy.
The thread in the top picture is a Coats 100% polyester thread. See how smooth it is?
The thread below is a Korbond polyester thread. This is fuzzy. And it melts if your iron is too hot too long.
I don't know what make this is because I have had it for years and I took the sticker off the spool. I only use it for basting and a bit of hand sewing now, until it runs out. I think it's cotton. It's really fuzzy and if you put thread like this through you sewing machine, you will need a lower tension setting, or the same thread on the bobbin.
As a side note, when you have run out of cheap thread for basting, it is really economical to use Basting Thread or "Tacking Thread" as some call it. You can get 50g (I don't know what that translates to in metres, but it's a lot) for £3.45. It's much better than using your good thread that costs £1.45 for 100m for basting! :)
Until next time, happy sewing!
The Sewing Corner