Last year it was definitely Portugal, but it seems to vary year to year.
Russia took a step backwards the last couple of seasons but I actually like the reason, top teams are pushing their young guys and giving them opportunities. This was a major criticism towards Russian clubs in the past, as they often preferred “proven veterans” even if their game was average.
Time will tell, but I believe this approach will have positive consequences in the future.
Another development about Russian League that could also be a significant boost is the fact that Dinamo and Rubin, two clubs who have fallen because of finances, seem to be climbing back up. At the moment, there are 5 clear “top clubs” in the league, but that could change next season.