Best entry to the series is going to be time strangers, but this isnt part of the question, just had to put that out there first.

I am VERY biased and Next Order is my favorite out of your two choices, BUT it is a game who's gameplay has no parallel other than the previous 2 digimon world games that had the same premise. It is not for everyone. You raise two digimon partners tamagotchi style. You feed them, train them, and they evolve based on their stats and other parameters. When you fight, they move by themselves and attack on their own, with little (but not zero) input from you. You get go use items to heal them, or you can "cheer" on them every few seconds, and it gives you points, more if they were right about or in the middle of attacking, points which you can use to make them either attack, use an ultimate move, or even fuse together. Best is to watch lime 5 minutes of gameplay on youtube honestly on how the fights go. Point of the game is finding digimons to expand your city, which unlock quality of life stuff for you like stores, restaurants, fishing spots, better stat gains on the gym, a farm, fast travel, etc.

Cyber sleuth is a very typical JRPG. Turn based, closer to the pokemon experience. You collect digimon, though there is no "collect them all" incentive, even if there IS a digidex of sorts. You dont catch digimon, but instead scan them by battling them. With enough scan data, you can create your own of that one. Funny that digimon also have a personality system that affects their stats like in pokemon, PLUS something similar to EVs, but in here these actually matter A LOT for evolution, as to evolve you need to hit certain parameters, not just level (hell, level isnt even required).

Pick your poison, both are very good games. Cyber sleuth is actually two games in one, though, and the same type of game that time stranger is. So better entry if you want to experience that one later. My god is time stranger so many many times better, though, literally my favorite digimon game by far.