As someone who has been playing piano for over 17 years as of now, I increasingly find that pieces I thought were "simple" in the beginning are actually much harder to play well, now that I actively know a lot more about the composers and more about the thought process they went through and how it should sound. So, I think there is a lot to be said about mastering a few simple pieces, but really understanding where they come from and how you interpret them because they set up really great building blocks for your future interpretation of other pieces.
Also, I would caution you from using or thinking phrases like "play them perfectly" because every performance is not without its errors or places where you think it should have gone differently. Master them to an acceptable level and move on.
So, to answer your question directly, I would stick with the simple pieces for now but not stress about playing them perfectly and gradually build up to the more challenging pieces you aspire to, rather than taking on a challenging piece right away. Especially when you're a beginner, learning a challenging piece takes much longer (in more crude terms: it wastes your time) than when you are an upper-intermediate or advanced player. Thus, often it's better to improve incrementally rather than try to take the big jump right away. Using the incremental approach, by the time you get to the challenging piece, odds are you are much better equipped technically and emotionally to deal with it.