How to determine which motors give me faster acceleration to a speed?
You can neglect the electrical time constants since they are so much faster than mechanical side of things.

You have an unusually large amount of information for your motors which is good because it makes this easy. Your load inertia dwarfs the listed rotor inertia of both motors, so you can neglect it. That means the motor with the most torque will accelerate up to speed fastest.

You don't need to consider the motor needing to accelerate itself until its rotor inertia becomes comparable to your load inertia. In this case, you would add your your load and rotor inertias together to get the total inertia. Then compare the ratio between torque and total inertia of both motors against each other.

In this case, the Series 9000 is about ~64000 torque/moment of inertia and the Series 14000 motor is ~60,000 torque/moment of inertia. So the series 9000 will get up to speed slightly faster.

Note that we can use just a single torque point here for this comparison rather than actually taking into account how torque varies with RPM and calculating out the exact acceleration over time because these are DC motors with a linear torque curve. It won't work for hold true for motors with non-linear torque curves (like induction motors). You'll actually have to calculate everything out in that case.

EDIT: Thanks to Phil G since I did not even notice that the datasheets listed electrical and mechanical time constants. I was just working on the generalization that electrical time constants are usually much much faster than mechanical ones. The time constants are actually a lot closer than I would have guessed, but the electrical time constant is still significantly faster.