Great question mcmillan.

I personally think that black panthers are the most beautiful large cats.  Their black fur is so exotic looking compared to other big cats.

Did you know a black panther is actually just a leopard, jaguar, or cougar that is black in color?

Below is a picture of a black jaguar:

What do you think is the most beautiful big cat, mcmillan?

When I think of big cats, I picture hot environments, like the African Savannah or the Indian or Brazilian Jungle.  That's why -- although it's not technically one of the "big cats" -- I am struck by the Snow Leopard.  Snow is just not something I naturally associate with cats.  These guys live in high in the mountains of central Asia, two to four miles above sea level.  They're very secretive, hunting only at dusk and dawn, and as a result, not much is known about their numbers and accurate taxonomy is difficult.  They are very comfortable with heights and can leap up to 14 meters to ambush their prey.  There is some amazing footage of a Snow Leopard's hunt on the Planet Earth series.

My favorite big cat is the snow leopard.  Unfortunately, their populations are extremely low and they are critically endangered.  They live in the mountains of Central Asia, and they are frequently the victims of poachers.  Their fur sells for a high price on the black market, and this is one of the major reasons for their low population.  The link below is a conservation website that explains why snow leopards are endangered and how you can help conserve this majestic cat.  

I think Jaguars are magnificently beautiful animals (and also one of the most overlooked of the big cats, judging from this post!). They are the third largest of the big cats (after tigers and lions), but are the biggest cat found in the entirety of the Western hemisphere. They are the strongest of the cats, with the sturdiest frame, highest muscle-to-weight ratio, and largest bite radius. For all that, they are among the gentlest of the large cats, preferring camouflage and solitude to expanding their territory through aggressive behavior.

There's also a lot of beautiful Native mythology about Jaguars. The cats often settle near bodies of clean, fresh water, a vital resource to the burgeoning Native American communities of South America. Living alongside these wild creatures, indigenous populations used their secretive, powerful beauty to think about questions of deep philosophical importance like the nature of power and human duality.

Therefore, for their beauty in both raw physicality and cultured spirit, I'm casting my vote for the Jaguar.

Like several of the answers above, I agree that the snow leopard is one of the most beautiful large cats in existence. Sadly, however, their number is diminishing. 

Oh, it is so hard for me to pick favorites! All large cats seem so graceful, with the combination of control and power of their movements.

I too love the snow leapord. But also think that Siberian tigers are quite beautiful.

I for one am a big fan of the cheetah. While not as big or as powerful as the other big cats, this cat has a sort of elegance about it. It is one of the fastest land animals reaching speeds between 70 and 75 mph. They can cover distances of up to 1500 feet during their sprints. Watching these cats hunt is a sight to see.

These snow leopard cubs are absolutely adorable. Their fur looks so clean and they appear so innocent.

I'm partial to the Snow Leapord. They have adapted their tails to be longer and thicker than other leapords. Their tails not only help them maintain their balance jumping from boulder to boulder, but they also act as a warm blanket and help protect their heads while they sleep. 

I gotta admit...I like the ones that'll take up half of the couch...

Fatty

I think the Clouded Leopard is the most beautiful.

Clouded Leopard

The ones that make me laugh!

Interesting question, and there are many right answers as it is all a matter of opinion. I too would say lion as I feel there is a beauty in its magesty, it's attitude, and its pride.  There is a reason, in fact, that they call a group of lions a pride. The male lion's mane is unlike any other, and despite their popularity, they are still most beautiful.

My favorite is the tiger. It is the largest of all the "big cats", and comparable to largest extinct felids. It can weigh up to 300 kg (660 lbs), reaching 3.3 m (11 ft) in length. This majestic animal has beautiful fur, with a pattern of black stripes over an orange back and white underparts. They are highly adaptable, living in wet mangroves, hot jungles, open grasslands, and cold taiga. A tiger can kill an animal as large as an adult rhinoceros. In a poll by Animal Planet, tiger came out to be the world's favorite animal.

I love the look of white tigers.  They are tigers with recessive genes that give them their lighter color (sort of like hair or eye color in humans).  They are not, contrary to popular belief, albino.  Some are even stripeless or a golden tabby color!

I think that panthers are beautiful.  I love their face structure, as well as their body form.  There is something about them that is both graceful and wild. 

I prefer the black panther.  The panther lives mainly in dense rainforests but is found in marshlands, swamps, woodlands, and several other places.  The black coat of the panther allows it to sneak up on its prey as well as hide from predators, blending in with it's surroundings with camoflauge. 

http://walking-on-fire.blogspot.com/2008_11_01_archive.html

I think that this cat is really interesting.  It looks like a cat that is out in the wild, but it is actually a housepet.  The domestic animal is medium to large in size, and originates from crossing the Asian Leopard cat with a domestic cat.

Cat

I for one just like lions. Also please look at my next comment

I think that the Siberian Tiger is the most adorable big cat.