So far we've heard almost nothing about Sega's mysterious Sonic Project 2017, but if it turns out like any of the other recent blue hedgehog-related releases from the company, it will probably end up on the lower end of "meh, okay I guess."
Conversely we have this indie project called Sonic Utopia, built by dedicated fans The Great Lange and Murasaki Fox, and it looks better than anything Sonic Team has put out in the last fifteen years. Seriously, look at this early alpha demo. This is basically everything I've wanted out of a 3D sonic game since forever. The Sonic Adventure series and Sonic Colors came close but Utopia is worlds ahead and it's barely even begun development.
Hopefully Sega isn't as big a killjoy as Nintendo--a company that actively DMCA's fangames that looks better than the official product (see: AM2R and Metroid Federation Force). The Sonic Utopia dropbox is unsurprisingly down at the moment but hopefully you'll be able to grab the demo soon.