I'd give the edge in both instances to Pluskal and Voronin and I imagine most others would agree. That's not to play either Zakarias or Modric down. And Zakarias did perform an important role for Hungary, offering some positional discipline in an otherwise gung-ho attacking set-up. But he's not the sort of player who is remembered particularly well. We hear about the eulogies for the magic five of Puskas, Czibor, Kocsis, Bozsik and Hidegkuti, but the defensive part of the team didn't have the same quality. And even despite having that profile of being in and contributing to such a famous team, he rarely features in many considerations of the best defensive midfielders of all time. In contrast, Pluskal has the really high praise, was recognised beyond his own team through the Rest of the World selection, and was clearly a standout player for Czechoslovakia in reaching the World Cup Final in 1962.
Same with Voronin/Modric. I rate Modric a lot for what he has been doing in recent years for Real Madrid and Croatia, very neat and tidy and a good all-round contributor. But I think Voronin brings more gravitas to the table: commanding, imposing, defensively robust, excellent on the ball, capable of getting forward to score a crucial goal (1964 Euros Semi-Final). He's probably in the top three Soviets of all time with Yashin and Blokhin, although happy to be corrected by the local expert there.