Typically the arguments go like this:
Straight:
1. Easier to get on target.
2. Easier to glass from above.
3. Easier to glass from a vehicle.
Angled:
1. Easier on the neck.
2. Easier to glass up.
3. Easier to use with multiple people of different sizes.
4. You can use a shorter/lighter tripod.
I use angled, because most angled scopes have a rotating color that more or less evens the field with the straight, except about getting on target easier. After some practice, though getting on target with an angled scope is second nature.