Anything within the mania standard (or VSRGs in general) is fine: 2-3 minutes, variety of rhythms (Recommending maps use songs from other rhythm games).
In the earlier stage it doesn't matter in which you want to focus on since you're still learning the fundamental, the moment you starts to go up to 3* and beyond you may want to check which specialty you're strong at and improve your weakness, since more specific patterns will starts to appear.