I am able to level 1 hero but am not sure who. I can ascend Sir Lancelot, Khan or Justice.
That depends on who else you have.
Are you ascending Khan or Justice to the final level and maxing?
Who else do you use in your current defense?
Justice is almost 2/60. Khagan is 2/60.
My defence team from left to right is: Grimm(12 emblems), Kash(no emblems.Li(3 emblems). Sartana(1 emblem).BT(8 emblem.
If it were me, I would make the decision based on whether or not i had the ascension materials to max Khagan and Justice. If not, it may be a better choice to have a deeper 4* bench first.
That said, I dont have much experience with Lancelot. I obatined him and Falcon at the same time over a year ago, and maxed Falcon, and still havent touched Lancelot. He may be better suited to stay where he is if you have better heroes available
As far as 4* heroes go I have:
Chao, Scarlett, Little John, BT, Li Xiu, Grimm, Kash, Kiril, Sonya, Wilbur, Caedmon, Wu, Tiburtus,Gaderius, Skitt, Cyprian, Gormek.
Unlevelled 4*: Danza, Gobbler.
To max: Hu Tao 3/60. Sir Lancelot 3/60.
For 5* heroes I have: Sartana(maxed) Grazul(maxed) Khagan 2/60. Justice almost 2/60. Another Grazul unlevelled.