It seems to be you still need some deep in your 4* red roster . Do you have another Bolstusk? A falcon or a wilbur? If yes id max them before continuing working with 5* stars.
Anyways from those you have the less desirable is Elena. Although she has the highest attack stat of all shes also fragile and slow.
Guardian Kong is a good offensive tool, a red that is fragile but at average speed and he hits hard too.
I havent try Lady Loki but ive heard good comments
This hero seems to be more balanced in stats that your other choices and in a status aliment meta with GM, Vela and telluria you can hit harder than those initial %150 of the ability
Im not sure what you mean. If you mean the defensive stat he has 690. Pretty high for a 4* star hero and much sturdier than kong or elena.
Plus you can combine him later with BT and other reds to make massive damage. I will give him priority. Hes cheaper and faster to level and you will have a game changer hero.
Otherwise , from the 5* you listed i will probably pick GK and being LK very close but more situational or meta dependent
What I mean that I have seen many raid defense teams had him and was quite easily beatable.
I will start maxing Wilber.
in case of 5* I m getting +ve towards GK now as his cleanse seems more useful.