Buy it for How you anticipate looking the most. (Down/even or up)
The general saying is lazy, road hunters buy angled, because they are usually looking up.
Guys who put boots to the ground, find themselves looking across canyons and down into canyons, and buy straight.
That's interesting most guys I know have angled and you primarily find us at the top of the mountains. Another hunter who you may or may not know, Aron Snyder, seems to be using an angled but he's known to be lazy and hunting from the truck. Honestly does that made up quote need to be added into a discussion. No offence but the idea of these forums is for information not to cause controversy go on social media for that.
As far as straight or angled there are definitely things that must be considered as noted above. I have used both and prefer the angled as it gives you the versatility to move the eyepiece so that you can be comfortable from 1 position and not constantly moving and adjusting to keep a full field of view.
If you are not in mountainous terrain or use your spotter just to identify an animal after spotting it with your eyes or binos, I would consider the straight as noted above it is easier for target acquisition and you are looking in one general direction. It definitely takes some time to learn how to pick up animals you have spotted with an angled but once you figure it out is a non issue. Also the eyepiece will not have rain/snow collect on it as easy as it could on an angled.
I find in the mountains of BC I prefer the angled. It allows you to sit in 1 position and look up and down the mountains and left to right. Again this is only if you are using your spotter to glass/grid. In a day I would say I spend no less than 2 hours behind my spotter so comfort and less movement are 2 very important things to consider. Moving the centre post up and down is not a big deal, especially if you have a decent tripod, when switching between binoculars and spotter or just to realign for full field of view. Were hunting so the less big movement the better. No amount of camo is better than less movement. Also as was stated above I have found that if you are hunting with others the angled is easier to setup for everyone to look into from one position especially children.
On another note you get what you pay for with spotters as the glass makes a major difference at higher magnifications. I would say use the cry once buy once principle when buying a spotter but also be realistic about your needs. I now use the Swarovski ATX because as stated before I spend a lot of time behind glass in heavily forested mountainous terrain in some really big country with point restrictions and counting rings, so the need for top tier glass saves my legs and precious time going after the wrong animal. I would buy the spotter that will fit your needs for the type of hunting you do and not for the once in a lifetime hunt, but for your regular hunting, as a guide will have the spotter or you could rent one from Rent Guns and Gear for those special tags.
Nothing new here, but consider your personal hunting style and areas and only use these as information to aid you in your decision. If someone says this is the best that only means it's the best for them. I hope this helps.