Power hacksaw or bandsaw

Neither, IMHO. I would do it the cheap fast way.

I would put down a tarp first.

Then I would attach a series of long worm-drive hose clamps around the tube and mark the cut edge with a felt tip pen.

Example:

Then I would remove the hose clamps and clamp the work *securely* to something that could not move.

Equipped with a face shield, hearing protectors and gloves, I would put a carbide blade in my circular saw to make quick work of the cut. This is where a smaller circular saw would be better. If the blade should grab the work, I wouldn't want a very powerful motor attempting to rotate the work away from me (or the SAW towards me!)

I would hold the saw at a perfect 90 degrees to avoid jamming the blade.

Aluminum chips would be ejected with force, so I would take steps to keep them out of my eyes.

Then I would shake out the tarp into a garbage can.

(This worked fast and easy for me in cutting cardboard concrete formers. The edges were very square and tidy.)

--Winston

Horizontal bandsaw?