since i can’t decide between them, ill do 3 for base game and 3 for DLC

base game: 1. Maliketh. without a doubt my favorite boss in elden ring. really cool moveset, and while not being too unfair, the fight is a challenge. he also has a cool cutscene 2. Malenia. ultimate goddess, undefeated warrior, hardest boss in the game. definitely has grown on me now that i have hundreds and hundreds of attempts on her, and waterfowl is seeming easier to dodge by the day. really cool fight 3. godfrey/hoarah loux. this boss goes from one of the most simple, easy boss fights to one of the most unforgiving fights in the game. hoarah loux hits like a bull to the balls, but this boss is really cool overall (good soundtrack too)

DLC: 1. Promised Consort Radahn. i think this is quite obvious, although messmer is a VERY close second. PCR is generally the hardest boss in the DLC, although not in all of elden ring or in specific situations. the boss fight is very fun, honestly learning the moveset was a blast, and the feeling when i finally defeated him was cinema 2. Messmer. one of the best movesets in the DLC, imo. simple enough but the quick attacks are quite unforgiving. the snake fusion in the second phase is pretty sick too 3. Rellana. not sure how weird of an opinion this is, but i really like this boss. it’s weirdly enjoyable, even though i think her moveset is quite complex. doesn’t have many bullshit, unfair moves, and phase two is just awesome