Anything making a contrail is at least 6 to 7 miles away, ( and that's if it's directly overhead, which most planes aren't; )
so with 10X, you're not going to get very much detail; the trouble with magnification is, it not only magnifies what you want to look at, but it also magnifies the slightest movement of the instrument you're looking through; anyone doing any serious "observing" with 10 X will have the scope / binocs on a tripod. And as I just pointed out, 10X really isn't ideal for viewing aircraft at that distance. ( if you expect to see very much )
If you plan to purchase something just for viewing, and not for photography, you may be better off with a good spotting scope. Many people make spotting scopes; the really good ones are fairly expensive, but then so are good binoculars;
The other thing you need to consider when deciding on what magnification to go with.......remember this; the greater the magnification you have, the more difficult it becomes to track a fast moving object; so right away, tracking fast moving jets is more difficult, and requires better support for the optics, than say, viewing a relative slow moving object such as a ship. (There's a lot to know about optics !) It's really nearly impossible to give very meaningful advice about something like this, without knowing more about ones budget, how much you intend to use what you buy, and exactly what you intend to use it for.
If I was going to buy a spotting scope for the purpose you mention, I would probably be thinking in the range of 15X to 20X Minimum
Spotting scopes come in many different magnifications; all good scopes have a fixed objective lens, ( the big end ), and an eyepiece or "eye lens" of a certain focal length; dividing the focal length of the eye lens into the focal length of the objective gives you the "power" or magnification; one eye lens, one power; if you have a zoom eye lens, you have a "range" of magnifications. ( probably the best way to go )
I would also want to have a scope with at least a 50mm objective lens; There's a HUGE difference between merely having the eye piece / objective combination necessary to achieve, say 15X, and actually "seeing" a decent, sharp image.
To achieve a good image, you need lots of light; (that's why anything less than 50mm isn't suitable.)
Assuming you plan to buy a spotting scope, you must decide between "zoom" optics, and a fixed focal length; actually it's different than thinking of camera lenses; all spotting scopes use a fixed objective lens, with either individual eye lenses, or a "Zoom" eye lens. Obviously, a scope with one eye lens and you have only one magnification; if you desire different magnifications, you then must choose between a zoom eye lens, or multiple fixed eye lenses.
Brands; many good ones to choose from, none are "cheap", but compared to, say, D SLR's, they may be "cheaper";
A few brands "stick out"; Leitz, Nikon, Swarovsky, Leupold, Fuji.......all make seriously good scopes; unless you have very deep pockets, I'd forget Swarovsky and Leitz; check out B & H Photo then look at all the Nikon scopes; you can get a really good 50mm scope for under $ 1,000 USD.
Another thing to think of; almost all makers offer scopes that are "straight", or with angled eye lens; for airplanes, an angled eye lens is a MUST. (try looking at something above about 45 degrees with a straight scope and you'll see what I mean)
Above all........understand this; all high end optics are "purpose built".........makers "aim" their products at specific markets; the markets for spotting scopes are : shooters ( straight scopes are OK
) bird watchers ( either straight or angled) multi-purpose ( definitely angled )
You will see many scopes at $ 79, $ 250 , even $ 500; I wouldn't buy any 50 mm scope that's less than perhaps, say, $750 to $ 1,000; to understand why I say that, you just MUST look through both; If you have recently won the lottery, I'd probably look at a great 82mm Nikon at around $ 5,000 to $ 6,000; ( They get expensive very quickly as the objective lens gets bigger !)
My very BEST advice; do not buy ANY optical instrument before you "read up", "educate" yourself about optics; then go some place where they sell them, and look through a bunch; (very important) don't buy the first thing you look at; and if you decide to plunk down over $ 500 bucks for anything with optics...........by all means, buy it from a ROCK SOLID source; for me, B & H Photo comes to mind;
Stupidity: Doing the same thing over and over again and expecting a different result; Albert Einstein