I think it's important not to value any specific metric too highly. But, the one that does seem to me to be the best, is PER, although it too has flaws. According to PER, Jack would be better than Blake, but I think that at least 90% of the posters here would disagree with that contention.
PER for the Blazers
EFF is another metric I look at sometimes, but it seems to be off the mark a lot. Like Roy this year had the 44th highest EFF, two ahead of Zach Randolph.
league EFF