Union is more CL.
Europe has its own CL between teams from England, France, Ireland, Wales, Scotland & Italy
Convicts, Kiwis & South Africa have their CL between themselves with their own club sides.
Everywhere else in the world Union is still pretty much an amateur sport, even Argentina who are one of the strongest Rugby nations, the sport is mainly amateur all their best/top players play in Europe.
League is only played professionally in England, Kiwis & Convicts.
Union has the more money, League has the better ball handers/runners/more athletic/harder hittin players than Union does. But has Union has alot of intricacies that differ from League like the rucks and mauls, scrums etc.
When the Union are running short on top players they raid the League code to get them because the players get a higher profile and more money. Some succeed some dont.
Hope this helps