First points we will added to offense or defense and some to regeneration.
These depends how you want to make that hero, offensive or defensive hero.

Do not put many points on offense or defense, it is sufficient 2-3 levels (10-15 points). These will help to pass over first period of the game.

Next levels you will added to Off-Bonus or Def-Bonus. Why?

I will explain this in a small example. We have 2 offensive heroes, each of them with level 25 (125 point):

  Hero 1 (Equites Caesaris) level 25:
    Offense:            0          (+)    0
    Defense:       100/130    (+)    0
    Off-Bonus:        20%      (+)    100
    Def-Bonus:         0%      (+)    0
    Regeneration: 125/Day   (+)    25

  Hero 2 (Equites Caesaris) level 25:
    Offense:          31350    (+)    100
    Defense:        100/130   (+)      0
    Off-Bonus:         0%       (+)      0
    Def-Bonus:         0%       (+)     0
    Regeneration: 125/Day    (+)    25

 

Army of the player is 5000 Imperians and 1000 Equites Caesaris.
Hero 1: 6000 Imperians(5000 + 5000 * 20%) + 1200 Equites Caesaris(1000 + 1000 * 20%)   
Hero 2: 5000 Imperians + 1000 Equites Caesaris

                                  + Hero power witch represents 175 Equites Caesaris.

 

We observe that in first case is much better, with a 9000 crop army. The difference will be bigger for some player with a 60.000 crop army.
The same demonstration can be done for a defense army.