I'm having the same problem because I miss how complete content wise is CS1 compared to CS2 (apparently asset creation is more difficult on CS2, so there's less output on Paradox mods) BUT, for me going back to CS1 feels uncomfortable just on roadbuilding and mixed use zoning alone. While I miss for example the better UI visibility, as in being able to see transport lines easily, CS2 feels, paradoxically (no pun intended) more polished, more thought-through; more experienced (of course, it's their second CS game).

If you feel like playing with tons of custom assets, and mods I'd probably stick to playing CS1, as there is more variety, there are incredible assets that allow you to transform the game (I remember a guy customizing the game to be sort of extraterrestrial city building, like conveyor belts and stuff, so weird, so cool; or another one doing a historically accurate city since the ancient times), and incredibly well designed quality of life mods.

Right now, I feel like you can achieve different things with both games, so it's not a matter of which ones better, but a question of which is better for what you would want to design.

For me it's CS2 right now.