Hard to say really! Learning elvish is generally very hard, much harder than any non-fictional language, the reason being that the only person that can say how the language works has passed away over 40 years ago... But as a beginner you can just indulge into one of the great courses that have been assembled and are presented in a similar style that you'd find for other languages.

For Sindarin the most recent one is by Fiona Jallings: realelvish.net - Store
For Quenya the most recent is still the one by Thorsten Renk, I think (he also has a Sindarin course): http://www.science-and-fiction.org/elvish/index.html#courses

After you're done with that you are ready to start exploring the many uncertainties there are about elvish and start comparing them and picking your favorite flavour of the languages.

I voted Quenya as the grammar and sounds were more similar to my native tongue (german). Sindarin has some concepts that area bit strange at first (mutations), but I don't think it's making the language significantly harder to learn. And yes, we know some more things about the grammar of Quenya than the one of Sindarin

Of the two major languages, there is more material available in Quenya than in Sindarin. I also think it is easier to learn.

That said, Sindarin is in some respects more popular, since it is the language more commonly used in (for example) Peter Jackson’s Middle Earth movies.

+Severin Zahler thank you :) that's very helpful!

+Paul Strack well, i really wouldn't know about that cuze i've only seen the hobbit movies once and some of the first lotr movie :') i read the books though. thank you for pointing it out! i didn't know sindarin was the popular of the two

+Dínen Sindarin was the vernacular (day-to-day) language of the Elves in Middle Earth (it was different in Aman, the Blessed Realm). Thus, in the settings of The Lord of the Rings, The Hobbit, most of The Silmarillion, and most of Tolkien's other works, Sindarin is in more widespread use than Quenya. In Middle Earth, Quenya was primarily used in ceremony, poetry, song, and important/high documents and names while Sindarin was used sometimes for these purposes and in nearly all other cases of Elvish speech. Tolkien called Quenya "Elven-latin" for that reason. I've found Quenya a closer fit to my personal aesthetic preferences and I appreciate the greater level of development that Tolkien gave it. Sindarin is also beautiful and elegant, especially its mutations in my opinion, and is said to have a "Celtic" flavor.

It’s always the parents objecting, isn’t it just? :) Quenya is by far the easiest language to start with, as we know so much more about it.