Good optics are preferable because of their high-quality scene rendition and even more critically for their minimal fatigue. Almost any tele-optic is useful for giving a distant open field or street a quick once-over. It is when you must study that field, street, or area of forest you want to navigate through that you will notice eyestrain and fatigue from mediocre optics.
The primary maxim of carpentry is "Measure twice, cut once". Get your measurement correct and you waste no lumber or materials. Even more apropos when haste or poor evaluation puts your life at risk. Quality optics are second only to your Defensive Firearms when it comes to tools that can safeguard your life.
Pretty easy to spend over $10,000 on "best glass" high-end optics. Zeiss spotting scope, eyepiece, Zeiss binoculars, Schmidt & Bender PMII 5-25x riflescope. Actually, the Zeiss classic 8x56 binos at $1700 are the most affordable and most critical of all three pieces of gear. If you wanted to own a "best glass" optic the Zeiss 8x56 Dialyt binocular would be a fine choice.
I'm not a big-game or trophy hunter who might spend $30k to finance a sheephunting trip to Alaska or a safari. Gonna spend that kind of money on recreational hunting, may as well own a fine spotting scope. I'm also not paid as a law-enforcement or contractor-sniper. Can't see circumstances where I will lay in a hide several days or many hours to make one shot on an enemy or perpetrator. Our military snipers use S&B and Premier Optics riflescopes. Europeans likely to choose Hensoldt, the military/tactical division of Zeiss. Great gear if you got the funding...
I can carry my spotting scope with 2" neckstrap and be halfway comfortable for the first hour. The scope is heavy though, and bulky compared to a binocular. Also typically requires fine focus tuning constantly. Perhaps this is simply operator-error, but the high magnification tends to focus the eye on specifics and thus requires more steadiness and relaxed position to make most of what spotting scope can offer. Binoculars, the best ones, offer independent occular settings. I set mine for an intermediate range rather than close or far. In dense woods, or other short-range situations this would change, but the independent ocular focus means pick up the binos and use them without fiddling or uncertainty.
The versatility of the binocular gives you immediately a fast scan tool for quick survey of movement noticed, or an irregularity. Also enables very deliberate studies. The quality optic allows long periods of glassing without fatigue, headache or other maladies. Like a pair of poorly-fitting boots, mediocre binoculars will cause you great discomfort and distraction. Distraction or failure to discern a well-camouflaged threat could end your career then & there.
Several types of binoculars are worth considering. A small folding set which will fit in shirt pocket will always be with you; like your defensive pistol, holstered and ready. The standard field-glasses size which vary from compact to heavy. Finally, the low-light binocular with larger than 50mm objective lens.
Zeiss and Leica compact binos are top-notch, but if you don't want to spend $650+, the Japanese camera-makers offer great product at affordable price-points. I found an 8x28mm set by Olypus on Ebay years ago and they're very fine, compact, and sharply resolving. Even the cheapies from Tasco and Bushnell are worth having to stash in a vehicle glovebox or bug-out kits. Also make nice birthday presents for kids when you can find them for under $20... Monoculars are also great for shirt-pocket stashing. Most any binocular can be separated and voila; you've got two monoculars. Just be sure each lens set has occular only adjustments.
In deep woods and other lowlight situations, the larger objective binos really do gather light more effectively. Zeiss Dialyt's previously mentioned for Best Glass Awards, but the 8x56mm Nightstalker by Steiner have been highly regarded for years. I have a Pentax set of 8x56mm that has also delivered good results even though they are a bit longer than I prefer. For under $700, there are few choices in quality 56/60mm objective binoculars.
For standard binoculars an 8 or 7 power is about perfect; 10x if your AO (area of operations) is mostly open without dense woods or vegetation. Best value I've seen are the Fujinon M22 mil-spec 7x50mm. A bit large, and a trifle heavy, but you can use these for hours w/o fatiguing and the color and contrast rendition is excellent. Zeiss classics would be a step up, but if you watch Ebay or other used-outlet sources, you'll find these superb binos well under $400.
First quality set of standard binos I bought were Steiner Military-Marine 8x30s. Great optics, but they fogged when the Fujinon's never have. Also have Zeiss 10x42 and 8x30 BGTP. Superb quality and compact, but the Fujinon M22s are the real workhorse go-to binos.
Testing binoculars before purchase is a must. You are looking for both close and distant fine resolution and most natural contrast. Test only in full daylight and choose the bino that gives you widest range of quality response. Buying used is not particularly risky, if the brand you select has a long-lived warranty that transfers to subsequent owners and you avoid any product enscribed with "Made In West Germany" if you expect a warranty. Germany was reunified almost 25yrs ago. Zeiss warranty runs 25yrs. Just a heads-up...