As stated above, it depends on use, but in general terms if they’re for carrying about on walks etc the ideal weight to benefit ratio is around the 8×32 mark. They’ll be compact, reasonably bright and clear. Anything much bigger than 10x magnification will be heavy, you soon get fed up with the weight and they’re hard to hold steady. (voice of experience….. my 10×42 Meoptas stay in the cupboard unless I’m out hill-stalking but the 8x32s are my absolute go-to pair) Don’t be tempted into anything with a zoom function, they really aren’t practical for carrying, and the unnecessary complication of a zoom system means constant faffing, more to go wrong and a lot of unnecessary weight.
The market is flooded with cheap binos, but here’s my two’pennorth:
Look at binos designed for the fieldsports market, in particular the manufacturers that also make sporting scopes and telescopic sights. The so-called “Alpha” glass makers such as Swarovski, Zeiss, Leica, Meopta, are likely to be out of your budget, but here are some fantastic runners-up;
Hawke
Vortex
Opticron
GPO
Meopta-Optika
Nikon
All of them make some really good binos, and the market they sell to is competitive and demanding, so at a given price-point you’re going to find stunning quality in terms of value for money , with lifetime unconditional warranties (Hawke and Vortex in particular)
How well each pair is suited to the user is down to personal preferences. For example, some work better for glasses-wearers as the eye-relief can be altered using the eyecups. Most do, but some eye-cup systems are more user-friendly than others.
This website is an absolute mine of information, and reviews based on budget. Well-worth a read
https://www.bestbinocularsreviews.com/