With the open beta release of Quaver, a highly anticipated VSRG(Vertical Scrolling Rhythm Game), the question has come up in the osu!mania community of whether or not to switch to Quaver.
To keep it concise, Quaver is better in almost every aspect except for charts and gamemodes. Quaver offers only 4K and 7K gamemodes, which are the most popular, but osu!mania offers 4-10K. Additionally, Quaver's selection of maps to play from is much smaller and more limited.
However, Quaver's mapping system is much more unique and fun, and the maps that do exist are way better than their comparisons on osu!mania.
TL;DR - Quaver is better