The three matches that I think are difficult to predict are:
Real Madrid versus Atletico
Bayern Munich versus Leverkusen
PSG versus Liverpool
I would definitely call PSG unlucky. Because they don't have a great record in the Champions League, and in the knockout stage, they drew against the strongest team of the season, which made their chances of winning very small. If they were against a team like Leverkusen or Inter, they might have had some chance of surviving in the league. But against Liverpool, it is almost impossible unless something happens.
The draw for the Round of 16 is going to be very competitive, which is almost impossible for a football fan to predict. Especially the Real Madrid vs Atletico Madrid match is going to be the most exciting. Their competitive game in the local league also makes La Liga interesting. They share the points in the last match. Let's see who can survive in the knockout match. Atletico Madrid may be ahead in terms of strength. But considering the overall situation during the match, one team will get a special advantage, especially in the second leg