transmission fluid change or flush?

I do not recommend flushes.

even though you don't get all the fluid out, you at least get the filter changed. so , you think that is adequate?

One benefit of dropping the pan is to see condition/life of the tranny by what the filter picks up , crud , bits of metal . there's usually a magnet placed in the pan to pick up any metal , Who ever drops the pan should pay close attention to the filter size , height from the pan , O-rings or anything else that may fall out .

Would you change the engine oil and not the filter? Same answer!

If you change the fluid every 30,000 miles you should not have problems.