Personally I used to upload at a bigger size and let the TMA software resize the image, but a change happened some time last summer which seems to have made the native resizing generate a less sharp image (it's also retrospectively affected some earlier uploads, which I mean to get round to reloading at some point).

Now I resize to 960 before uploading, which seems to retain the sharpness better. The other advantage is the upload seems to be quicker and less prone to not working, which used to be a problem sometimes when I used to upload at a bigger size.