I’d go with sideways, with the sub in the right corner.
There are many benefits.
The surround speakers will be some distance from the seating, which always sounds better than rear speakers too close.
The sofa will be close to a wall, which will result in bass levels being perceived as louder than they would at the other options. The other options have the seat basically center of the room, which is the worst location for bass. The center of any room is kind of a “bass hole,” and bass levels increase as you move from there towards any boundary.
In addition, bass levels will be more uniform in all seats on the sofa compared to the other arrangements.
Regards,
Wayne A. Pflughaupt