Here is the spreadsheet we keep up-to-date with all the info we have about the game. It is sortable so that you can filter/sort monsters by any category you care to.
It also ranks all monsters by Health / Attack / Rest and Total Stat Average. There is also a column to compare each monsters individual stats to a cat of the same level. The cats were chosen for this purpose as they are generally recognised to be the most useful of the main island monsters.
There is also a tool to allow you to calculate how much experience you need to raise a monster to a certain level or what level you can reach with a particular amount of boost materials.
Link to public collaborative spreadsheet: