I do find 'subject aquisition' much easier with straight, which most of the time is a non-issue...but i've had experiences where a particular animal is in view for a matter of seconds, and guys with angled fail to get on it before it disappeared....and in some cases, getting that view decided go or no go
another thing to consider is that if you ever use abinocular off a tripod, it is again much quicker to swap back and forth between glasses and spotter without messing about with adjusting the tripod too much
i guess as well, i just prefer a straight view of things, not 'around the corner' if you know what i mean
but some of the pros of angled listed above are certainly worth considering...most particularly the point about the 'steep uphill'!!