If Boldtusk is your first one go with him. You need to have a solid floor of 4* first before going with 5*. Generally a 4* at max is better than a half 5* (aka 3/70)
There are top 4* star heroes that are so useful that even having a solid bench of 5* dont exclude players to keep running those 4* along with their 5* . This is bolstusk case
Good luck!
PD: This i comment is based on what i see in those pics , if those 4* are dupes and you already have them maxed so i will probably go with Anzogh which pairs good with wilbur / Boldtuk and Falcon if you have them.
Otherwise Jean Francois is a good defensive and support hero.
Lastly the slow ones , Azlar and Elena.
If your 4* are not maxed yet before doing a 5* do
Boldtusk
Wilbur
Scarlett and
Sumle
Lancelot is a good choice too
Was thinking scarlet as be better on titan have read up on lance but that was ages ago, I can clear epic events only thing I care about is getting a certain level so get the we flasks.