Question about Canon EF 1.4x III

Why do you want the converters? You have to bear in mind that the 1.4 costs you one f-stop, the 2.0 two f-stops. Accordingly, the exposure time increases or you raise the ISO. You also have to bear in mind that your camera or lens no longer supports AF above a certain aperture stop. Your question as to which is more sensible cannot really be answered. Best regards

As the previous speaker wrote: the 2x converter costs you more light and also some sharpness? If you need the focal length (200x2x1.6=520mm KB equivalent), then take the 2x. If you don't need it, then I would go for the 1.4x.
With the 2.8 output aperture you won't get problems with the autofocus that quickly. Two f-stops from 2.8 is 5.6 and that should not be a problem. There are overviews of which focus fields work in which camera-lens-converter combination. You can find them in the manual for the 80D from page 128 onwards. The focus areas do not differ (both group B).

The sensor of an EOS 90D has a much higher resolution than the 80D. Maybe that's enough for you.
I use a 90D with the 1.4x converter and a second generation 100-400 mm. The bottom line is 900 mm. I use it to take handheld pictures of kites circling over our house, with 9 cross sensors still active for AF. The images are perfectly sharp. And thanks to the high resolution of the sensor, you can zoom out very well.
I don't know the 2x. I bought the 1.4x because of the autofocus, that was important to me.
I used to have a 2x and a 1.4x with Carl Zeiss lenses on my Contax, and you couldn't tell the difference in sharpness. But that was a different world in terms of lens quality...

Thank you very much for the answers. I should perhaps have specified my question a little more precisely. I was only concerned with the technical differences between the products on offer. I was confused by the different presentation of the images, but the same price! Since I need the converter exclusively for documenting a swallow colony (occupation of the nests, frequency of approaches, etc.) and the equipment is fixed on a tripod, the autofocus is not relevant. I should also be able to cope with an open aperture of 5.6. And I hope the loss of sharpness is kept within limits. An alternative would be a 400 or 600 tele with f 2.8....But if I were to order such a lens here, I would have to add the cost of a divorce...and then it would get really expensive! I have therefore decided to go for the 2x converter. Thanks again!