Consider the following

1) Need physical keyboard? Mac.
Yes, iPad also got keyboard but that's a seperate accessory so you got to spend more.

2) Does your software runs on specific OS? If so, choose the one that runs on.

3) What if both OS also can? Choose the one where people have said it's easier to use on.

4) Screen size. 15" or you're good with the max of 13"?

5) Do you need OLED? Is that really important or just a good ol LED is enough?

6) (Programmer) No brainer to just get the Mac as you can't run XCode on iPad.