There doesn't seem to be any rules as to which you should use which can be confusing. I've seen, for example, "for" being used interchangeably with "av" and "pa" being used interchangeably with "til." So when I have to translate the sentences into English, sometimes I get them wrong because I've used the wrong preposition. I try not to "cheat" by clicking on the hints.
English prepositions, however, are always the same and are easy to use. Which is why I said I wasn't sure that Norwegian was easier than English (but Norwegian is certainly easier than German lol).
My first language is Portuguese and although it's a fairly complex language, we have one magical preposition that can be used (even if not formally correct) to express "in," "on," and sometimes "to." For this reason, I always struggle with prepositions in other languages. I've lived in a foreign country where I speak French and English on a daily basis for the past 8 years and I still make mistakes. By the way, in Portuguese we don't make a distinction between magic/magical, mechanic/mechanical, historic/historical, and to me that may be the hardest concept to grasp in English. I really can't tell if I used the right one in the beginning of my comment...
I haven't seen any sentences where you can just chose one preposition or the other. They've always depended on the sentence. Like, the idea of "for" is usually for, but "for" a length of time is i, except if you haven't done something "for" a certain amount of time, in which case that's på. Each one has quite a distinct usage; it's just not a one-to-one correspondence with English prepositions.
Prepositions are notoriously arbitrary, and don't have easy inter-language equivalents.
Compare Norwegian with Chinese, where you don't really have prepositions at all. There are coverbs that work like prepositions, and some nouns and adverbs that work like postpositions. So, you say the equivalent of
- "I reaching Beijing go", where "reaching" is a coverb that conveys the destination, to say "I go to Beijing".
- "I being-at Beijing live", where "being-at" is a coverb expressing location, to say "I live in Beijing".
- "That plate being-at table top remains", where "top" is a postposition, to say "That plate remains on the table".
- "He leaving the house interior came out" where "leaving" is a coverb indicating origin, and "interior" is a postposition, to say "He came out of the house".
Whatever's your native language is probably what feels easiest to you. But as a foreign language, Norwegian has been a far shorter learning curve than any other I've learnt (and this is, I think, about the seventh one I've studied seriously...?). And it's creating a bridge to German, which is brilliant because it was starting to frustrate me.
A language picked up from birth is going to be significantly easier. The infant/toddler brain is uniquely programmed to acquire languages.
Once you're out of that sweet spot of easy language acquisition, the difficulty of learning additional languages depends on your native language. Norwegian is coming pretty easily to me, because I am starting from English, a relatively closely related language. It was much harder for me to learn Russian because the Slavic languages aren't as closely related to English as the other Germanic languages.
Učio sam hrvatski u četiri tjedna, i jer nema veliki razliku izmežu hrvatski i srpski ( osim ćirilica ( ponekad ) ), mislim da srpski nije vrlo težak jezik.
It's rusty, but learning that was nowhere near as hard as studying Polish, ( or Russian and Slovene / Slovenian ). In my experience, Serbo-Croatian is probably the easiest Slavic language out there.
I am German and learned English in school many decades before. From my point of view norsk is much easier to learn, because it is much closer to German than English, but after one year of learning norsk I am still not able to "think" norsk. I read Aftenposten and listen to several podcasts daily and sometimes watch shows on Netflix in norsk. Reading is not so hard, but I frequently need to lookup words I did not learn using duolingo. Podcasts and shows on the other hand are hard to understand, because none of them speaks norsk, all of the Norwegian people speak dialects, depending on the origin. Some are understandable, some not. Without norsk subtitles I would get lost. By the way: "Forklart", "Klar tale", "Historiepodden", "Fortell meg om" and "norsklærer karense" are my favorite podcasts.