Tbh I just like how calm and collected Darth Vader seems. Especially whenever something goes wrong. Compare that to Kylo Ren's childish temper tantrums and you'll be able to understand why I've always sympathised with Vader the most out of any character. That said, I've always leaned towards the Empire than any other faction. Mostly because they are incredibly disciplined, structured and efficient. Other factions have always seemed so chaotic and unstructured to me.