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In late summer, I came across a test-report that introduced optics and mechanics of (at least) twenty binoculars. The best (since you asked for "the best") were made by Leica, Zeiss and Swarowski but you'll have to pay an arm and a leg for one of those.
The cheapest binocular rated "good" was Eschenbach's Trophy AS/D 8x32 B, but I guess EUR 280 is still too much, and you'll probably need a 10x binocular.
I don't know what power you'll need for spotting airplanes but I always thought the Nikon Monarch was a great binocular and a great value. I've seen the Monarch line in magnification powers from 8 to 12 and a number of lens sizes (although I'm not up on the particulars of what exact magnification/objective combinations are available).
The 8x42 is a great all around binocular spec and is produced in the Nikon Monarch line for less than $300. A 10x42 is available for $300.
On the other hand if by "spotting" you're simply looking to distinguish airline type and registration numbers you can probably get away with a cheap pair. I don't mean to plug Nikon too heavily here but I've never been disappointed in one of their products. I am sure other good value brands exist as well.