For me, it's cinnamon and nutmeg. If I could only have one, it would be nutmeg. I grew up in Louisiana, and the combo of the two appears in lots of dishes, including desserts, sweet potato and squash casseroles.
I grow all of my main go-tos. Nothing like going outside to get some fresh herbs to add to the meal; especially soups & roasts. Basil Oregano Thyme Sage Parsley Rosemary (Yes, I've got the whole song, plus.) I have to harvest the basil all the time, or it gets too big. It nets about a tablespoon of dried basil/week, plus all the fresh I could possibly use.
Dill I can live without it, but its pretty much the only spice I use. Also occassionally garlic powder.
How are they different? I don't use paprika much, mostly to make garlic bread look pretty Also, deviled eggs.
If I had to choose just one spice, I'd choose Adobo seasoning (primarily garlic, but with salt and pepper as well). If I had to choose a second, I'd add Cajun seasoned salt (Tony Cachere's or Zatarain's). Basically, I like salt, garlic, pepper, oregano, basil, and hot peppers. Also cumin and chinese 5-seasoning mix.