So, how do you choose a flavor that everyone will like? Or should you only choose one flavor? Here's my advice.
Stick to one basic flavor for the bride's cake and if you have a groom's cake you can do something a little more unique or taste specific. By choosing a traditional white cake or maybe a yellow or spice the majority of guests will enjoy it. Punch it up with a yummy fruit filling and you are good to go! Use your groom's cake to be the cake with the more taste specific flavors, like a black forest or red velvet cake. There aren't as many servings, so you aren't wasting cake that goes uneaten. Plus, guests still have the more basic bride's cake to choose from as well.
But what about having each tier a different flavor? Well, a bride can certainly do that, but I personally don't recommend it. When the cake is cut they begin at the top and serve the entire top tier. Then, we move onto the second tier and serve that and so forth. Therefore, your guests will not actually get to choose what flavor they want. They are served whatever tier is being cut at the time they are in line. Not to mention, the top tiers will only serve a few people, so just a handful of people will get certain flavors while others are left to the larger tiers. When guests see another guest walking around with a different flavor sometimes it causes guests to go back for seconds to sample that new flavor, and there is a possibility that you can run out of cake. Or, what if that flavor is gone? So disappointing.
All that to say, I personally recommend only serving one flavor per cake to keep things simple and your guests happy. Too many flavors can cause confusion and chaos at the cake table.