Which multimeter can measure accurately PWM 30kHz duty cycle?

[Kiriakos GR]

Since the beginning of digital multimeter, best way to classify them was … multimeter for electrical work and or a multimeter for electronics.

Pulse-width modulation = electronics application
The measurement of Duty cycle at PWM signal, this is a task for special in design handheld DMM.
Even so only when you do attempt to use any handheld DMM so this to measure Duty cycle, you do get clues of its product actual performance and or limitations.

PWM Measuring requirements:
Bandwidth 25 ~30 kHz
5V pulse signal

From the list of compatible HH DMM, we have Keysight U1272A and the BRYMEN BM869, but only one can do it accurately.
And this is the U1272A which has significantly highest accuracy along bandwidth.

BM869 this found to be significantly inaccurate despite of it higher bandwidth.
Also BM869 this has a bug, at over three volts of Pulse signal, Low battery alarm this activates, but this is a false condition.
BRYMEN is aware of the issue for several years, and they do not bother to fix it.

INTEL PWM actual specification for bandwidth this is Target frequency: 25kHz, acceptable range 21kHz to 28kHz.
Absolute maximum voltage level: VMax=5,25V (open circuit voltage).

Duty cycle measurement this is actually a job for medium priced oscilloscope (700 EU or better).
Oscilloscopes are not bandwidth limited as is digital multimeter, and I will recommend, if you plan to do product characterization, to use both as comparison point, U1272A along the oscilloscope. 

[overvolt]

From the list of compatible HH DMM, we have Keysight U1272A and the BRYMEN BM869, but only one can do it accurately.
And this is the U1272A which has significantly highest accuracy along bandwidth.

This explains of is why you got three U1272A..     
For three phase Duty-cycle testing. 
 

[Kiriakos GR]

From the list of compatible HH DMM, we have Keysight U1272A and the BRYMEN BM869, but only one can do it accurately.
And this is the U1272A which has significantly highest accuracy along bandwidth.

This explains of is why you got three U1272A..     
For three phase Duty-cycle testing. 
 

True 

But for the vast majority of my readers, I will SIMPLY remind that BRYMEN this is good quality at budget price products.
Keysight U1272A this is not a budget price product for a hobbyist.