It doesn't really matter how many levels your ability have. It actually depends on what you are doing.
Standard maps have 3 normal abilities with 3 levels each + 1 ultimate ability with 1 level. Your hero has max level 10 so that way you end up eventually maxing out all your abilities.
Some other maps have for example max hero level 16 with 4 abilities where each ability (even the ultimate one) has 4 levels.
I also saw some maps where you had 5 abilities each with 5 levels, but your maximum level was 15, so you needed to consider which abilities you want to max and which you don't, etc.