There are a couple of southern hemisphere competitions which you might add to your Union list -- the level of play in New Zealand's ITM Cup and South Africa's Currie Cup isn't that far below the Super-15. As for money -- well in Europe it's not even close. For example, English SuperLeague clubs have a basic salary cap of 1.6 million pounds per season. In the Aviva Premiership it is over 4 million pounds. French clubs pay even more. The upshot is that any League backs (particularly those in England) who are good enough to play in the Union game gets immediately snatched up by a Union club. Loose forwards as well, presuming that they can learn to perform adequately in a lineout. Tight forwards aren't a factor, as they haven't really existed in the League game since they abandoned the contested scrum. Of course either of these sets of salaries seems pretty small potatoes when compared to those of the top Association Football clubs.
Japan Top League (Rugby Union)
French top 14 make the most in union. I have no idea about league though.
