I switched back and forth between both for years. Modern is more smooth and scooped, recto has more aggressive mids - a "bark" so to speak. Initially I preferred the modern, for more (surprise, surprise) 'modern' type metal sounds, but moved onto the recto when I wanted something to cut through the mix more. And the Modern is definitely quieter in volume.
In my opinion neither were among the best MTS modules (stock, at least).