| The Boosta Grande is a little flatter - both of them have a tendancy to thicken up the low-mids a touch, but the BBE is closer to being transparent. The MXR adds a little sparkle up top, as well. They're both superbly made and sound great driving a tube amp into overdrive or as a volume boost for breaks and leads.
You'd be hard pressed to get me to choose between them, especially since they're almost the same price. It's more a question of if you're looking for something more transparent (BBE), or you want something with its own colour(MXR). | 
