title_body: I like a really mild tasting coffee, not to bitter, a little bit sweet but not overly sweet, what beans have this kind of flavour
upvoted_answer: I think your question may need a bit of disentangling, however I will try and deal with your main points. First there are several factors that influence coffee bitterness, and origin, albeit important is not the most influential factor. More on that later. Secondly it is not clear what you mean with "mild" coffee. Do you just mean "not bitter"? Because non bitter coffee is by no means necessarily mild. It can even be more flavorful with very fruity flavors and a lot of acidity, while bitterness may cover up a lot of these flavors.
  Regardless of that I will now write some points about how to reduce bitterness.
  
  
  Arabica tends to be lower in bitterness and astringency than Robusta, because Robusta contains more caffeine and chlorogenic acids. So take care you buy 100% Arabica.
  The roasting is a very important factor. Dark roasts are much more bitter than light roasts, while lighter roasts emphasize floral, fruity flavors and acidity. In my opinion most people who complain about bitterness in coffee could fix that by drinking lighter roasts. Unfortunately for most people roasted coffee has to look dark brown to almost black with a glossy surface. In most cases beans like that are over roasted. So  you may want to try your dads beans with a different roast profile.
  How do you prepare your coffee? Bitterness is often a result of over extraction. Make sure you extract your coffee properly so you get a flavorful, but delicate and pleasant taste. You will find instructions for your preferred preparation method here on the stack exchange, on many websites of specialty coffee shops or you could ask in your favorite specialty coffee shop.
  Last but not least, origin can play a role in bitterness. Overall you could probably say (all else equal) that many african coffees are lower in bitterness and higher in acidity. You could try Ethiopian and Kenyan coffees. Ethiopian coffees tend do be very delicate, floral with nice acidity while Kenyan coffees are higher in acidity and fruitiness. Central or South American coffees are probably (all else equal) slightly more bitter, but if the roast and extraction is right, bitterness also shouldn't be an issue. They would have more nutty, chocolaty flavors. Of course there's exceptions. Panama Geishas would be relatively high in acidity compared to other Central American coffees (also much more expensive and the bean is originally an Ethiopian heirloom variety).
  
  
  To sum it up though I would recommend you first focus on point one to three. In my opinion they are more influential here. I'm assuming that you are already using Arabica, but I suggest to try different roast profiles and recipes. If you already did that I would recommend you to buy some washed Ethiopian beans as they produce delicate (you could maybe call them "mild" although I don't think it's the appropriate term) cups.