Assuming that I'm using fixed IV's for CBC mode and CTR mode. I know that in CBC, the blocks depend on the previous ones and on CTR they are all independent. Yet with the same key and fixed IV, the system wouldn't be secure in CTR and with fixed IV same plaintext would be converted to same ciphertext which causes another security issue. Even though I know these, I cannot decide which would be more secure when I use fixed IV's. Any help is appreciated.