I've owned dozens of excellent overdrive pedals over the years, and for the past 2 years had settled on the Strymon Deco as my favorite - the most amp-like, most natural, most unobtrusive. Recently, I picked up Greer Lightspeed and I gotta say, it's just as good! Now I have 2 really great grit boxes on my board, so I put a video together to see exactly what the differences are.
Basically, the Greer is a little bit brighter and the Deco has all the other features - slapback, chorus, & flange. The Greer is analog, and the Deco is digital. The Greer is Pink, the Deco is silver, etc.