So it seems obvious that these two will benefit a lot in an iron hand army.
So if you had to choose between the two as your army center piece which one would you choose?
From my perspective any of the two will be a priority target for your opponent and we can use them as a brick shield that will absorb all firepower coming at them.
I guess the obvious weakness if being tied up in combat by hordes or very strong multi damage units.
In that sense both offers a very strong firepower source in our army (the leviathan probably better at killing T7 tanks, MEQ hordes such as intercessors)
but the executioner have the Fly keyword which is very valuable.
The problem I see is that even if on the paper the executioner seems to be a better choice it is still going down with some strong firepower such as many las-cannon shots where the leviathan is almost un-killable with the half damage stratagem and the relic.
Also the 20 shots and two heavy flamers with overwatch on 5+ should be more than enough to finish a horde trying to block them in combat with the help of some character heroic interventions.
What is the best choice?