These days colour processing using funky effects is used way too often in an attempt to enhance a mediocre image. Instagram and other smartphone apps seem to have exacerbated the issue, but used appropriately, colour processing combined with other post processing can enhance an image.The key is to start with a good image, and then depending upon the end goal look to see if it can be improved upon. This might be to make it look more like what you actually saw when you took the photo, or it might be taking an artistic view.
The centre image of the nine images below is my original photo processed for realism. The outer eight photos are different interpretations. My tool of choice is Adobe Lightroom, which comes with a number of processing presets, and it's very easy to select different ones and see the effect. It is immediately obvious that some presets just don't enhance an image, and may degrade it. However, there will be some that do enhance the image, and Lightroom's ability to make virtual copies allows me to make several versions of the image processed in different ways. Below is a selection of these, some made simply by applying presets, others by applying additional effects such as a vignette, and lastly one using the paint brush tool to paint colour back into the stamen (top right).
Which is the best is purely a matter of the viewer's taste. Ironically, I actually like the montage as a whole rather than favouring any individual image over another.