One thing to consider is exit pupil size because it is a major factor in cost, size and weight. The exit pupil is the diameter of the lens divided by the magnification. For example, 7x35 binos are 7x with 35mm diameter lenses. They have a 5mm exit pupil.
You will see exit pupils as high as 7mm (ex. 10x70). A large exit pupil is beneficial if you are young and are using the binos at night or maybe deep dusk. The idea is that your eye's pupil has a certain diameter for any given ambient light level and by matching that diameter you maximize the amount of light transmitted to your eye. If, however, your pupil is dialated to 3mm and you are using 7mm exit pupil binos, much of the light is wasted. During the day, you should not see much difference between 10x70's and 10x40's. A young person, in pitch dark, and dark adapted, will have a max of a 7mm exit pupil. As you age, your pupil size recedes to about 5mm or so.
For daylight use, I don't see any sense in going past 4mm or so, especially for your (portability) needs, because your eyes will be dialated and even if you are viewing something in deep shade, where more light might help, you are probably in bright enough light that your eyes are dialated to 4mm or so. All that extra glass (and associated weight- and cost) is wasted. Take that into consideration when you pick your binos. If I were picking a new pair, I would go with something like 10x40 or maybe 15x40-50 at the largest, depending on what magnification I wanted. I might go with something like 10x30 to cut weight, size and cost, but I would want to pick them out in person.
If you go with a higher magnification, you need a progressively larger diameter lens to maintain a 4mm or so exit pupil. If you go too much lower the image will be dim. You should try some out in a shop to see what exit pupil you are most comfortable with. Because of the portability issues, if you go much beyond 10X you may be trading magnification for a brighter view. For the same reason that it is much more enjoyable to shoot with a fast F/1.4 lens rather than a slow F/5.6 zoom, sometimes a brighter view, within reason, is better than a highly magnified but dimmer view. I don't want to argue decimal points with anyone, I'm just trying to be vague enough to say that you need to try them out before you buy and to understand in a general sense the real life trade-offs behind the numbers.
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Regards,
Neil
