Good question. My first MCC 03RG20 (in 2005) were fantastic, but after that I've had batches which weren't impressive in terms of burning quality, then I've seen again some very good results around, so consistency plays a role here, more than with MCC004 (despite some consistency issues mainly with the MII ones).
But the point is, good MCC 03RG20 burns @8X just as well as MCC 02RG20, is easier to find, and seems to have a wider proper support in most recent burners than 02RG20.
Now being slightly OT:
Both MIDs have equal reading compatibility in my experience. The reason why I prefer 02RG20 is not burning quality, but their outstanding stability. Both C't climatic tests and my own degradation survey of my discs, show that these discs can probably live up to the manufacturers claims (and could well outlast me). They share this perfect stability, in my collection, with TTG02, CMCMAG E01 and probably (a little to soon to be sure) MBIPG101 R04. All my other MIDs show, at least with several individual discs, some kind of slight degradation (in most cases nothing alarming - just noticeable). Yes, even YUDEN000T02 in some instances (but frankly, nothing to worry about).
Granted, this apparent superior stability of some MIDs could well be due to other factors, like minimal impact on scanning variation from pass to pass (excellent reflectivity? Excellent mechanical properties?), who knows, but with the data I have at hand, they just seem to have something going for them, with this absence of variation in consecutive scans after 6 months to a year. And stability is certainly the main thing I'm after for my own discs.... way more than fantastic PIE/PIF scans.