For some extra thought, lovelod: As you can see here Ember Spirit has 19 + 2 Str gain and 22 +1.8 Agi gain, so eventually Str catches up.
But the difference is quite small: for your level 22 it is only a 2-point difference (61 vs. 59).
I would very much recommend becoming familiar with the hero stat gains. This will help you pick heroes to better suit what you want to build with them. Also just as, or even more important,
is cast time, attack animation (look under "Advanced Statistics" on the link above).
Ingame you can see these statistics when looking at a hero in the tavern if you have "Enhanced Tooltips" option checked in the Gameplay Menu.
Hope this is helpful for you, cheers
Edit: Of course, the ingame hero may not be the same statistics as from the website above, since it's 2 different games, maps, versions, and they might not be the same. But that was just to show you. I hope this was not confusing, sorry.