I like how the first game has slightly better character customerization than Conquest, where we can manually enter the hair and eye color of our w̶a̶i̶f̶u̶ starting slave, and Conquest only have a very limited pool of more 'realistic' color selection. And of course, first game has wider age selection between child, teen and adult while second only have teen and adult. But second game have a few more species to do pokemon collection if you are a completionist and enjoy this kind of thing.
Second game's food system is definitely better than the first one though. How easy it is to get more food than you can eat has been a pretty sore point I had with first game, since the lore of the game says slavery became wide spread because lack of food... but in game play it's so easy to get more food than you can eat if you know what you are doing (pump agility into yourself and your starting slave and do 'hunt'/'gather' task), it might as well not have been a mechanic at all.
I like second game allow a party of 6 compared to the first game's 4, since the more the merrier. First game has better traveling system though, since it has an actual map giving a sense of where everything is instead of a simple drop down menu.
Not much on story side since second game's story mode isn't finished yet. So far, I like how the first game blend mechanic tutorial into actual story (not going to spoiler the ending for anyone not completed the first game's storyline), while second game have promise of more political drama down the pipe. I grew up on Romance of the Three Kingdoms, so I always enjoy more GoT style political drama in a story.
Overall, both game have their own strength, at least so far. Conquest obviously have more potential since it's only... what, half way finished?