German, like English, belongs to Germanic language family, so it is similar in vocabulary and grammar. But German grammar is very complicated, and there are many things to remember, so I won't say it here.

Spanish, Italian, Portuguese are all Latin, and of course French. Their ancestor Latin attached great importance to inflections of nouns and verbs, so those languages inherited this habit. Comparatively speaking, Spanish is the simplest in Latin, and the relationship between Portuguese and Spanish is just like what people in China say, with different pronunciations and some subtle differences. So I think Spanish is better.