This is a statistical fallacy. Two blocks will always be equally difficult when they were mined with the same target.
This is a definitional fallacy.
What you mean to say is that clients prefer to choose the block with the least block hash.
What you mean is the most difficulty, which is not the same as the numerical block hash. The natural numbers less than 2^256 are a total order, but difficulty is a partial order on block hashes.
Let's say I have two hashes: 0xF000 and 0xEFFF. Target is 0xFF00. Then: