Gütermann, Coats cotton (not Coats Moon!), Presencia, Superior Threads and YLI are good brands.
For most ordinary sewing you need polyester size 100/3, or for 100% cotton use size 50/3.
You only need thicker thread (lower first number) for really thick fabric such as denim or machine quilting or very fine thread (higher first number) for very sheer fabric such as voile.
Rayon threads are for embroidery, and not strong enough for seams.