As others have said, without knowing your other heroes, we are just making generalizations.
Boldtusk is a very good healer and tank.
Grimm is one of three 4* heroes available from legendary training with Ramming Pulverizer which debuffs defense for 6 turns ( very long for a buff or debut ).
Caedmon is one of two 4* heroes available from legendary training with Piercing Strike which removes all enemy buffs. I only fight 5* Titans ( no clue about 7*+ titans ) so it is mostly useful in raiding/ war.
I like healers, and Boldtusk is a very good one. In fact he doubles as a tank. With a healer you can complete more rare quests, completing more rare quests get you more ascension materials which let you level more 4* heroes to 4.70 .
Grimm has the lowest defense and HP of 4* Heroes with Ramming Pulverizer, but his attack stat is the highest. It’s 6 turn duration really helps the rest of your team, especially if you can debuff the titan or a triple boss.
Caedmon has the lowest defense and HP of 4* Heroes with Piercing Strike, but his attack stat is the highest. The permanent nature of removing enemy buffs is nice, but unlike the other two heroes it is a reactionary move. If the enemy has zero buffs, you don’t need to remove them. While the other two ( healing+ attack buff, splash damage+ defense debuff ) are useful no matter what the enemy does.
So just based on the information in your post, I would choose Boldtusk.
Edit: Boldtusk’s attack buff stacks with Wu Kong and the heal helps keep him alive
Sabina ( basically a purple clone of Melendor ) gives you a second Wu Kong healer ( see above link ) and clears enemy buffs like Caedmon. But when you eventually level Melendor you can swap out Sabina and Melendor depending on the situation.