Between those two, whose grammar, vocabulary, or pronunciation is closer to English?
Is there any other reason?
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I don't think that your question can sensibly be answered solely by reference to issues about grammar, vocabulary or pronunciation. Some people find that they simply cannot pronounce certain sounds in another language; others find that they manage the new phonology OK but have difficulty with various grammatical differences.
That said,there are several Wikipedia pages that might help you. In addition to the general Polish language page on Wikipedia, there are additional, more detailed pages about Polish phonology, Polish orthography and Polish grammar. Yet another level of detail can be found in the page on Polish morphology. Similar information is available on Wikipedia about the Portuguese language, its phonology, grammar and other aspects. It is only by considering in detail the various differences between the multiple aspects of each language (degree of inflection of nouns, adjectives, adverbs; tenses and moods of verbs, etc) that you might have any possibility of predicting your own individual difficulty in learning either of the two languages.
However, if instead of taking an individually tailored approach to the decision, you are willing to rely on generally available empirical evidence, you might consider the fact that the Foreign Service Institute (on the basis of its experience in training hundreds of people to speak foreign languages) rates Portuguese as a Category I language and rates Polish as a Category III language. What that classification means is that, for most native English speakers without specific prior foreign-language experience, it will require 600-750 hours of training to become a competent Portuguese speaker but it will require around 1100 hours of training to become a competent Polish speaker.