The music which makes you say, "Gosh, I wish I'd written this!"
The music it is most important to your development as a composer that you study is the music that you love.
(This is apparently not obvious to a lot of people. It wasn't obvious to me. So I make it explicit.)
Now, if you're starting out, you may want to put that on hold until you've picked up some analytic skills on music that it is easier to do that on. This of course depends on just what your favorite music is. If you think that Clementi's piano sonatina Op 36 No 1 is the pinnacle of human artistic expression, I have great news for you.
What makes music "easier" to analyze is not really a property of the music itself, but rather it's proximity to the type of music for which the analytic terms and concepts were designed to describe.
A quarter century ago I took my college's "Harmony and Counterpoint I" class, because it was the pre-req for all the subsequent theory and composition classes. I want to share with you what the instructor said to us that first day. She said, in res,
In this class we're going to cover the basics of what is termed Common Practice Era (CPE) voice leading. The CPE is basically the core period of classical music. We're teaching you to write harmony in this style of music not because it is superior to others (because it is not), not because it is more important than others (because it is not), not because it is more sophisticated than others (because it is not). We're teaching you to compose in this style because this style has a rigorous, thoroughly worked out method of composition that is easy to teach. And for that reason, classes on all styles of music typically use the terminology and concepts from CPE voice leading, even when the rules of those other musics are completely different. That is why this class is a pre-req: to give you the musical language needed to participate in those classes.
So I'd like to suggest that if you're totally new at this, and if you haven't covered that material yet, that you do likewise. That you take -- either in person, or through self-study with textbooks and/or the internet -- an intro CPE voice leading class, and analyze whatever they tell you to, however they tell you too.
Then you take those tools, and start applying them to the music you love -- though if it is music that is from a different genre, then you will have to adapt them. You will have to treat the rules you learned as hypotheses to test. You will have to take what you learned, and ask, "how closely does this piece that I love follow these rules?" Because the ways that they don't are part of what gives them their characteristic sound.
If you've already covered the basics of CPE theory, and you're ready to start applying that learning outside the CPE, come back with a question about analyzing a specific piece and we'll see what we can do.