That's a tough one! It truly depends on personal preference and how you value each player's particular shooting attributes. However, based on their career stats and overall shooting percentage, it looks like Roberto Firminho has the edge in this respect.
When considering their overall career stats, Firminho boasts the best shooting accuracy of the three with an impressive 57.8% shot accuracy. Notably, he averaged 0.41 goals per 90 minutes in the 2019/2020 season as well as 0.5 goals per 90 minutes during the 2018/2019 Premier League season.
Jonathan Sh also performs admirably with a shooting accuracy of 54%, though he slightly trails Firminho in this respect. However, what he lacks in shot accuracy he more than makes up for in his ability to create chances; he has a stellar assist record of 0.21 per 90 in the 2019/2020 season and is a threat in the box on both attack and defence.
Finally, Pim Rush has the lowest shot accuracy of the three at 46.2%. However, he is the most dangerous in front of goal, averaging 0.56 goals per 90 minutes in the 2018/2019 Bundesliga season.
From the above stats it seems clear that Firminho is the best marksman out of these three players with the strongest shooting accuracy and most goals scored per 90 minutes. Ultimately, this is an incredibly difficult question to answer definitively and asking other football experts for their opinion could be an interesting exercise for validating your own.
Hope this was helpful and good luck with your decision!