Well i have played both and dynamic tend to focus on training points, peformances and their traditional growth curves. For example, last night i scored a free kick with shimizu and his fk acc. went up and curl in the next 2 weeks. Also, Modeste was averaging a goal a game in the epl so his shooting stats went up. However the downside to this is if a player plays bad - sloppy passes, losing possession, own goals and low ratings mean the player by decrease or stay the same however he can increase again.
E.g., David Jarolim, reborn and 18yrs old had a rating of 80 o start up with and due to poor peformances, he went down and i looked like i was destroying his carreer however next season he asisted lots and scored some cracking volleys so now he is 81 and 20 and i hopei can rebuild him into one of the best players.
But they can also increase if you train them manuelly and set alll players focus points
However, the other players not in your team just develop there normal growth curve and it don't depend on their peformances.
So personally I would go for dynamic because it is more of a challenge so if i score a good goal, it won't really matter as i wont increase on it and instead follows my normal growth curve
I hope I have helped you understand and i look forward to see which one you chose
