What is the best way about choosing hero to keep and what hero's that u should use to be consumed by other hero's
Deploy them in raids and dungeon raids. They gain xp which then level your heroes. Once you have them at level 20, you can use HB points to level their stars so you can level them further.
Generally, a hero levels according to what start you have unlocked for them. There are 9 stars (or tiers) that they can progress through, each consisting of 20 levels thus giving us a maximum hero level of 180.
Here are the basics:
(1) All heroes start at 1 star (or tier 1) once obtained/hired,
(2) They must be maxed out in the previous tier before being able to advance to the next. I.E. to go from 1 star to 2 star, the hero must be level 20. 2 star to 3 star, the hero must be level 40. and so on...
(3) Heroes are upgraded using the Hero Alter, and a combination of Gold (consumable), Honor Badges (consumable), and Flames (similar to Trophies, are NOT consumable, and they are earned by completing dungeons).
Hope this helps!