My Suggestion (December 2013)
If you use a scope extensilvely then save up for a high quality scope with a diameter of about 80mm to get lots of light to a 20-60x Zoom eyepiece. I have always used Kowa scopes, and they are up to par with Zeiss and Swarovski. But try them out because you might not like a feature like the large focusing ring on Swarovski and some Nikons, making your choice a little easier. If you want to go with a cheaper scope like Kamakura then be sure to carefully compare with the other scopes in low light (e.g., evening comparison).
I rarely use a scope and like to travel light so I use the tiny Opticron Mighty Midget Travelscope. I use the 40862M HDF T eyepiece with the MM2 V2 ED which gives me a 12-36x magnification. But I have noticed that sometimes I really would like a larger scope to get the higher magnification. So my advice is to get a Kowa or a Zeiss with a 20-60x Zoom!
Large vs. small
The more light the better has been the guideline especially when using highpowered oculars, zoom oculars or when digiscoping. Scopes with a frontlens diameter of 65mm or more is advisable.
The costly high end versions of some scopes (indicated by APO, ED, FL, or HD) are first appreciated when using the scopes in difficult, or low light situations,coupled with zoom oculars or when digiscoping. But they are worth the extra money since the most common setup today is with a highpowered zoom ocular, and they will last for decades.
Angled vs. straight
There is really not much difference between the two models. Tha angled is great if you are sharing a scope and don't want to adjust the tripod all the time.
I grew up with the angeled scopes and cannot say much about the straight scope. But I have found or gotten on to birds just as fast or faster as the English chaps with their straight versions.
In raptor migration a straight scope could be to your disadvantage as the birds can travel quite high, and you need to bend your neck awkwardly to keep them in view. But I think the differences are too small to say that the angled or the straight is a clear winner.
Zoom vs. Fixed ocular
In the past Zoom binoculars, and Zoom oculars were synonymous with a poor image. This is no longer true. The Zoom oculars for large diameter, high end spottingscopes are often excellent.
You can Zoom out to 20x magnification for scanning wider areas, and when you want to look closer at a bird simply Zoom up to 50-60x!
If you rather want maximum field of view then a fixed ocular will be best. You should pick a magnification of 25x to 35x. One of the most common, and best fixed oculars on 72 to 80 diameter scopes is the 32x Wide Angle.
My Suggestion (October 2012)
If you just want a picture for your records, or for pure documentation then don't forget that mobile phone in your pocket! It always comes with a camera these days, and you can often get a picture through the eyepiece of you spotting scope.
Zeiss has a nice page about digiscoping.
Traditional digiscoping is still the most common method when photographing stationary birds that cannot be easily approached. It is easily done using a small compact digital camera photographing through the spottingscope eyepiece using a simple adapter.
The preferred scopes have a front lens diameter of 65mm or preferably larger to collect as much light as possible for the Digital camera. The adapters can be made by yourself through some guidance from the trailblazers on the web, or purchased in most large spottingscope stores.