If we are to compare these bowlers in a meaningful way we have to dissect their stats. Jamieson has a small sample size so I expect his stats to get worse with time.
Bowler stats vs the top 5 test teams:
Cummins: Innings - 71, Average - 22.07, Wickets - 177, SR - 47.8
Cummins has amazing test stats as expected.
Bumrah: Innings - 48, Average - 24.63, Wickets - 100, SR - 55.3
Note that I've only used Bumrahs stats vs the top 4 test teams because he hasn't played Pakistan and 5th best team in his stats is Sri Lanka which I don't consider one of the top teams. Overall very good stats.
Rabada: Innings - 71, Average - 24.37, Wickets - 179, SR - 44.1
Very good stats but he's still slightly behind Cummins in the test format. The most impressive thing about Rabada is the number of wickets he's taken at just the age of 26.
Jamieson: Innings - 20, Average - 18.89, Wickets - 47, SR - 45.9
Jamieson has had an amazing start to his Test career but I wouldn't put him up there with the other three just yet. He's yet to face Australia Which i going to be his toughest test and we'll see what he's made of then.
Just like with Bumrah I've only used Jamieson's stats vs the top 4 test teams because he still hasn't played Austria.
Bowler stats vs the top 5 ODI teams:
Cummins: Innings - 61, Average - 30.07, Wickets - 97, Economy - 5.31, SR - 33.9
Surprisingly Cummins has every good ODI stats against top teams. I expected his average to be over 35.
Bumrah: Innings - 48, Average - 34.43, Wickets - 62, Economy - 5.01, SR - 41.1
Overall Bumrah's stats aren't that bad other than that horrid strike rate for reference Dale Steyn had a strike rate of 42.3 in test cricket. On the plus side, Bumrah has a great economy rate.
Rabada: Innings - 46, Average - 29.39, Wickets - 73, Economy - 5.16, SR - 34.1
Out of these 4, Rabada has the best ODI stats which is surprising considering no one talks about him when they talk about the best ODI bowlers around, about time that changes.
I won't be sharing Jamieson's ODI stats because he hasn't played enough matches to have reliable stats.
Opinion and rating:
In Tests:
Cummins > Rabada > Bumrah > Jamieson
In ODIs:
Rabada = Cummins > Bumrah
The reason I think the other bowlers are currently better than Bumrah is Bumrah's strike rate in both the formats. All the other bowlers strike rate in test cricket is in the mid-40s whereas Bumrahs strike rate is in the mid-50s. The same thing in the ODIs Cummins and Rabada's strike rate is in the low 30s whereas Bumrah's strike rate is in the low 40s.