I did not take the current level of your heroes into account for writing this piece of advice.
Titans
Usually players use heroes with specific special skills during titan fights. Which heroes exactly depends on your hero-bench and the color of the titans. I will include examples, but not all that are out there. The specific special skills usually used during titan fights are:
Healing / Healing + Removing Status Ailments / Healing + Debuffing / Healing + Attack/Defense Boosting
Boldtusk (H+AB), Rigard (H+RSA), Kiril (H+A/DB), Melendor (H+D)
Other examples with these abilties
Sabina (H+D), Ares (H+Crit Boost), Hawkmoon, Belith (H+D), Vivica (H+DB), Aeron (H+RSA)
Attack/Crit Boosting
Zimkitha (A), Ameonna (A)
Other examples with these abilties
Ares (C), Gregorion (C), Brienne (A), Khiona (A), a couple Atlantis heroes (A/C), Wilbur (A)
Defense Debuffing
Gormek, Tiburtus, Isarnia, Grimm
Other examples with these abilties
Wilbur, Valen, Ulmer
Elemental Defense Debuffing
You don’t have any hero with this ability
Other examples with these abilties
Guardian Falcon, Guardan Jackal, Guardian Panther, King Arthur, Evelyn (December’s HOTM)
Wu Kong
No explanation needed, right?
Other examples with these abilties
Tarlak
Let’s take a red titan fight as example. The heroes I would definitely include are:
Kiril (H+A/DB), Isarnia/Grimm (Defense Debuff; maybe both) and Wu Kong.
Depending on your playstyle and titan special attack, you choose two or one more hero(es). Options could be Triton (healing boost + sniper), Magni (defense boost + sniper), Rigard (extra heal for survivability + removing status ailments) + Ameonna (purple attack boost, stacks well with Rigard or on yellow titans), Proteus (mana control for survivability), Inari (dodging for survivability), Justice (blinding for suvivability) etc. You get where this is going.
All that matters is the type and color of the titan. One thing for sure; I would always include Wu Kong until you get Tarlak.
Raid attack
The best thing you can do is to adjust your attack team to make it strong (color stacking, special skills counters) against the heroes you are going to attack. In order to always be able to do this, you will need quite a few heroes to choose from. You have a significant amount of heroes with different abilityies, so it will be possible once you have leveled them up. I would however recommend to level up 1 hero of each color at a time.
I would also recommend to focus on building your titan teams. With the heroes you level up for this aspect of the game, you will already be able to pick heroes based on the heroes you are going to attack. Mana control heroes and fast snipers are very useful during raid attacks.
Some of your heroes I would definitely bring with me during raids are:
Boldtusk, Gormek, Grimm, Tiburtus, Rigard, Proteus, Zimkitha, Magni, Triton, Kiril, Sonya, Caedmon, Melendor, Li Xiu, Marjana
Raid Defense
Same story here. I would recommend to focus building your titan team first and use the heroes you have maxed (or leveled) for your raid defense team.
Some great heroes for a defense team are:
Isarnia, Marjana, Boldtusk, Elena, Proteus, Rigard, Cyprian, Justice, Li Xiu, Magni, Kiril, Boril, Kashrek, Caedmon