For baked or roasted red or gold potatoes, I love them with olive oil, chopped garlic, salt, pepper, thyme, rosemary, and paprika, topped off with parmesan cheese. That's my go to but I like to experiment as well, I'm definitely gonna try something with curry powder next time...
For sweet potatoes, my favorite way to have them is with butter and soy sauce. I know it sounds weird but the flavors balance out and it's soooooo good.