I have a straight Nikon ED82 - for me holding my head at an angle for any length of time = neck pain. I chose and use the scope primarily for observing from a fixed position for periods of time - mostly seawatching, waders, and waterbirds - and find it does the job very nicely [the big zoom is very good for this, but that's another discussion!
]. It was my first proper scope, and I partially chose straight as I knew I'd have trouble getting on stuff [I'd tried out a few scopes and realised just how big a difference it makes being able to point straight at a moving bird, rather than line up with a sighter, then look and find you're already off-target]. Another advantage of straight not yet mentioned is being able to look down on things [from a hilltop/cliff etc.] much more easily.
I also have an ED50, which is straight too, and is my 'mobility scope'. I don't even use a tripod with it - either in the Grippa case in the top of my rucksack when walking, or on a shoulderpod for close terrain - great for treetop warblers! Again the straight helps with handheld, as you can pretty much look down it [though the eyepiece is slightly offset, its easy to compensate]. A factor with the ED50 is that due to the different prisms the straight body transmits a few % more light than the angled [I'm waiting to be corrected here, aren't I?], but I'm sure that's not the case with all scopes [again awaiting correction!].
After babbling on, I'm going to conclude with the famous birding optics cliche - try out both, and see what works best for you, and what you want to do with your scope.