So right now it doesnt make a huge difference what you play. You're still at the point where all your learning is how to hit the right key when you see a note.
If you want to practice more specifically, dont be afraid to try some higher ranked maps. What you need to practice is learning the really basic kinds of patterns. Look for maps with more than 1 note at a time, or rhythm you find difficult to time correctly.
The most important thing is to make sure you are playing maps made for mania mode, not standard maps that can automatically convert to be played in mania. To do this you have a few options. You can type "mode=m" into the search ingame. You can also set the sorting to sort by game mode.
This is important because the rhythms make more sense, the patterns make sense, and you will see lots of patterns in mania only maps that you will never see in converted maps.