The new ECC83 MG has slightly lower gain and is designed to suit for extended clean tones and more headroom with guitar as well as with HiFi audio amplification.
With the JJ EL84 tube you seem to get a compromise between tone and reliability. Nice mids, sparkling highs and solid bottom end characterize this tube.
This Slovakian tube has colorful lows, loose-easygoing mid body, and a brightly shining chime for the highs. In overdrive, it offers a tight and focused bite with crisp, bright, and well-defined articulation.