...and you wanted to buy TWO pair of bins, which would they be and why?
Why, have you won the Lottery and are at a loss as to what to spend the money on?
Should they be two pairs of the same model or different?
Well, I think this could be like buying hi-fi audio (one of my other passions): there's not a unique maker/model/size that's universally and objectively perfect. At that stage, only what you deem and feel to be the better is what's actually the best for you, nobody else can tell you. It's not unusual to hear apparently silly reasons for having chosen any model, but that only shows how subjective this is.
There are some relatively simple questions though that you should strive to answer before beginning to benchmarking, so you can focus on YOUR really relevant contenders:
- Preferences on magnification/field of view: What magnification do you like? Some birders prefer the wider view of an 8x, I'm used to 10x
- Your favorite birding locations: Where will you typically be using the bins? In your past experience, how are typically light conditions in the corner where you bird at most? What have you missed at most in the past?
- Your favorite birds: What kind of birds do you like/watch at most? I mean, in which kind of landscape do you typically find them? Are they usually close to you or far away as raptors? Are they colourful or rather brown?
- Your typical trips: How long do your trips take? Could weight be a "more than usual" significant issue?
Once you've got a better concept on what will you look for, check at the tests and comparisons given by birding related organizations, so you can maybe make some basic interesting findings. I've got for instance valuable information at the Cornell University's site regarding spotting scopes.
The last and maybe most time demanding task is to test: test every bin you feel it could be a choice, even not been the top class ones. As you will most likely (but not necessarily) be looking among reputable and very renowned makers, you can demand more convincing test chances at the stores, even taking some units with you for a weekend. At this stage, you should make some meaningful notes on those fulfilling your expectations. Afterwards it could become harder to remember how the feeling was.
Last but not least: Just a condition I've taken into account when looking for my optics (even being money an issue for me): Consider only eco-friendly makers. Most of the top makers are, but it wouldn't be wrong to check what materials and finishes do they use. Some tests have shown that even the best optics makers sometimes have disregarded this issue. Check e.g.:
http://www.test.de/themen/bild-ton/...410164-1410136/
This is rather old, but on the column "Schadstofffreiheit" [freedom of hazardous/pollutant substances] you can see most of them have become a regular note (3.0).