Wall>Fortress>Barrier and maybe the strongest is the Ultra rare one, but still didnt found any of it, but hardly farming with "premium"... after 6 hours still not a single fortress or anything with 20% extra from tech center, just walls, some gold gen and useles arcane... yesterday I found 3 Aries AND 3 legend too without any bonuses or the premium :/
Also I want to ask if there is any may number of rare unit?
I just want to ask something interesting, why is the "common" Defensive Wall stronger than the more rare Infinite Fortress? truly, that 25% resist is nothing, cause with 5 Neg Voider you have 115% negate for all of your stuff, I suggest shield or extra hp instead of that useless stuff.
 "Dragon Fortress"){kind=icon}
 "Enigmata: Stellar War"){kind=icon}