The test I like to do on a riflescope is near sunset (with the sun about 5 degrees above the horizon) look below the sun at a hillside which is not being directly illuminated by the sun. Internal refelctions are what kills contrast in any scope (rifle scopes, spotting scopes, and binoculars, and that is an acid test. THe percent of light lost going though a scope is only really important if it's scattered inside the scope and comes out of the eyepiece so it washes out the imaage you're trying to see.
But in a riflescope the MOST important characteristics in my opinion are that it will hold zero during rough treatment, like being dropped. and that the knobs track orthoganally, linearly, and accurately. in the units they're marked in. I don't look for a picture window view. I want a decent field of view free of chromatic and spherical aberatiion. I want it not to fog up internally.
Most of my scopes are Leupold, a few Burris (pistol mostly), a few Bushnell (mostly on ARs), one IOR, a couple of Weaver, and even a couple of really junky Chinese scope (Leapers and BSA). none have what I would call bad optics, but what makes me pay $1000+ for a Leupold over a $100 BSA is it's mechanical properties and ruggedness, not it's optics.
My favorite "long range" scope? The Leupold Mark 4 16x40 mil-dot. Why? It's rugged. Relatively light weight, has excellent eye relief, and a huge elevation adjustment range (140 MOA). I use a laser rangefinder, not mil-dot for ranging but the mil-dots are handy for quick wind and range "holdoffs " without cranking the target knobs with a simple lookup card. My favorite "best buy" scope is the Bushnell 10x40 mil-dot for most of the same reasons. It's under $200 while the Leupold is over $1000.
In my opinion one should always match the rife AND the scope to the task at hand witout reguard to price. More expensive is not always better. I'm not above putting a $4000 Litton scope on a $400 CZ 22LR or a $250 Leupold on a my $5000 Pauza carbine if they do the job best.