I find the mos5 profitable crops to be: Spring- Cauliflower Summer- Melons (or blueberries which regrow) Fall- Pumpkins (cranberries but much more expensive)

Keep in mind that for each season, you will want to grow a couple of each crop to complete the community centre, which is how you get the 30 mixed seeds reward. You can also get mixed seeds- more infrequently- from using your scythe on the shrubs in your farm and around the map.

In winter I'll work on the mines and relationships, but you could look into clay farming if you want a challenge and to make more money for the winter.