You have a bunch of good heroes to work with. I agree with @Keyz about maxing Wu ASAP. He is instrumental in high titan scores.
As to your other questions, there isn’t really one single team. Some heroes are good for defense but not for raids or titans. Others are best on raid attack. Some excel on titans but aren’t as good anywhere else (looking at you, Wu). You’ll want to tailor your team to your opponents.
For a defense team, you could use Grimm, Boldtusk, Li Xiu, Rigard, Caedmon. Grimm is a little squishy, but in the corner he is protected, and his defense debuff will make your other hitters more effective. Boldtusk is sturdy and boosts attack. Li Xiu is also sturdy, but slow. She needs to be hit with lots of tiles for her special to charge, so tank is the best spot for her. Her mana cut will delay your opponent’s specials. Rigard is also sturdy and slow, but he is the best 4* healer bar none. He also cleanses, so he can get rid of negative effects and damage over time on your team. Caedmon is a good strong sniper who also dispels enemy buffs.