Cone Coffee Filters or Flat-Bottom Coffee Filters?
Cone filters or flat-bottom filters isn't usually a major decision since you just use whatever your coffee machine is designed to take. Any differences between cone coffee filters and flat-bottomed coffee filters (also sometimes called basket filters) is going to be fairly subtle. But the general opinion is that cone filters create a deeper layer of grounds, meaning that the water is in contact with the coffee grounds for a little bit longer. This means that coffee brewed with a cone-shaped filter can be stronger than flat-bottomed coffee. It can also mean that cone-brewed coffee has a greater chance of being bitter if left to brew for too long.
But if you want to switch filter styles, you will need to get another coffee machine because they are constructed to use a certain type of filter and that isn't something you can change. The majority of drip coffee makers take the flat-bottom coffee filters so you may need to search a little bit to find a cone filter machine if that's what you're after. Several Melitta coffee makers use cone filters and they are the main company that does use them. Whether you use cone or basket filters, you will need to know the right size for your coffee maker. They may all look alike, but there are minor differences in size from one machine to another. For cones, they are numbered so you can easily look for #2 or whatever size your machine takes. Getting the wrong size can mean a poorly brewed cup of coffee, or having loose grounds end up in your cup.
When buying paper filters, you can usually get either bleached (white) or unbleached (brown). The unbleached ones are better for the environment and it doesn't have any impact on your brewing whatsoever. These options are available for either cone filters or flat-bottomed filters.For an even more environmentally-friendly choice, and one that will save you money in the long run, you can buy a reusable filter instead of paper ones. They are usually made with a fine metal mesh, often plated with gold (or just "gold-toned" metal). They come in both cone filter and flat-bottomed filter shapes, so you should be able to find one to suit any machine. It fits inside the machine's grounds basket just like a paper filter would. Though it saves you from having to buy and dispose of paper filters, a permanent filter means you have to empty and rinse it out with each pot of coffee you make. Not a huge inconvenience but it does lack the quick disposability of a paper filter. The choice is yours.