Translation:Cable television is still the best option.
To me the English translation is weird. I think it needs to say something like "Cable television continues TO BE the best option" or Cable television continues as the best option"
As cloudhorizon says, although your translations have a more literal feel, the meaning of "continues to be" is simply "is still". This link has a few more examples of sentences using "continuar" and when appropriate (as in this case) "still" is used in the translations: http://pt.bab.la/dicionario/portugues-ingles/continuar.
I think that's a more literal translation, yeah. But in my opinion the English sentence sounds perfectly fine. I think that's what most people would say too when speaking to others.
Na minha humilde opinião, não há televisão a cabo, mas, televisão POR cabo...
Is it the positioning that distinguishes "better" from "best"? i.e., "the better option" = "a opção melhor"
I would say it is actually the difference between "a melhor" and simply "melhor":
For this sentence to be translated with "better", for example, it would have to be something like "Televisão a cabo continua (sendo) uma opção melhor"... or "...uma das melhores opções" (one of the better options). The "uma" is not always necessary: "TV a cabo é melhor" (cable TV is better). I hope this answers your question. =]
Is this also a good translation:"Televisão a cabo AINDA é a melhor opção".