Rarity is a character that is beautiful in every way, may it be physically or from a character standpoint.
Rarity cares a lot about her physical appearance and wants to be in the spotlight, but at the same time she also wants the same to be true for every other pony. She creates things of pure beauty with her limitless imagination and creativity, and instead of hoarding what she herself desires, she shares it. She makes other ponies feel special and fabulous, even though she could focus the fruits of her art on only herself, she choses not to, because making others shine in the spotlight is something she loves.
She does want her place at the limelight too, but she wants to share it with everyone. Share it with her friends... With the whole world. Make the whole world more gorgeous.
Its that limitless passion and drive to make others happy, let them shine, that lets her work beyond her physical boundaries. She shares a lot with Pinkie actually, as both make other ponies happy, just in different ways... Pinkie and Rarity have more in common than one can see at first.
And like Pinkie would never throw a inferiour or half hearted party, Rarity would never deliver a hastly sewn together dress made from shoddy material. Its a matter of pride on the one hand, for she is very proud of her handiwork, rightfully so, but also a matter of wanting the best for others. She works herself to be bones... Sheds blood, sweat and tears.
Thats a sign of her generosity. She wants the very best for others... Make them feel like a prince or princess even though it might cause herself discomfort or harm, and it actually did very often in the past, like in Suited for Success for example, or Green isnt your Colours.
Yet Rarity does not hold grudges, even though she had reason to on occasion. She could have been angry at the mane6 in Suited for Success, yet she blamed herself. She was able to forgive Blueblood for his uncouth behavior and even baptised his airship. She was forgiving of Sweetie Belle when she printed her diary in the newspaper, and was the only one to explain to them what they actually did wrong, instead of shunning them.
She is just an incredibly forgiving and sweet pony.
Yet, even thought she is caring and lovely, she is also brave and strong. She, who is a delicate and somewhat sheltered fashion designer, was the first one in line to kick a full grown manticore in the face. She roundhouse kicked Applejack, one of the physically strongest of the mane6 into submission when she was discorded. She kicked flank against the changeling hordes like all of the ponies, not scared to chip her hooves in the slighest.
If something needs to be done, she is not scared to get her hooves dirty, and that weights even more than for example Rainbow or Apples, because Rarity has a really crippling fear of dirt. If some evildoer need a good thrashing, she will not hestitate.
But her physical capabilities are not all weapons she commands over, she is also incredibly cunning and smart. She easily saw the biggest weakness of the diamond dogs and exploited it, and when the rest of the mane6 tore through the ranks of the mutts with force, she already had them feeding out of her hoof the whole time.
She was generous at first to actually search gems for them, but when they made clear that they were to treat her like a slave and not let her go again, she used her wit. And that quite successful! much more than she could have accomplished with punches!
Her intelligence can also be seen in how successful her business is, for she had to build up all she accomplished by now all alone. She did not have help of the rest of her familiy like Applejack, or did not grow up in a advantageous environment in Canterlot like Twilight.
Yet she managed to become one of the most famous designers in all of Equestria despite her youth and inexperience. She just knows how to handle ponies and business!
But even though she had no help from her familiy when building her fashion empire, she dearly loves her parents and her little sister, as difficult as they may be sometimes.
She has nothing but sisterly love for Sweetie Belle, and had so already in the past, like Sweete Belle Toils showed. She threw herself in the mud for her, and even though their relationship is sometimes a bumpy road, they will always travel it together, and will catch each other if one stumbles.
Rarity is very forgiving and generous when it comes to her little Belle, quick to forgive her misdeeds, and its the same the other way around.
Even though she has many virtues, Rarity also has her flaws. And these flaws make her the realistic and rounded character she is, for without flaws a character would be boring.
Some people might see her as selfish, but i disagree strongly. Rarity is not selfish or greedy, but she can be rather self centered, which is not the same at all. She sometimes forgets that the things she enjoys and loves are not automatically the things others might enjoy, and even though she has the best intentions, some might not like the spa as much as she does.
She can also come across as uncaring to some, but she is a very caring pony and shows that she is though her sacrifices and her gifts. Its just that sometimes she flat out fails to notice certain things, like for example that she sometimes fails to notice Spikes struggle to impress her, even though she cares for him greatly, and showed that she does a lot.
That does not happen out of malice, but sometimes she just does not notice because she is busy with other things, is in an creative surge for example. When Rarity is focused like that, i imagine it like a trance, the one thing she has her mind focused on is overwhelming at the moment, and all other things have a hard time of keeping up it.
She is just an artist, and like many of them she has her eccentricities.
All in all, her virtues are much more prelevant than her flaws. She is a sweet and generous, beautiful and caring pony. Full of passion for her art, her friends. Passion for love and life.
She is a great rolemodel, and a pony that everyone would be happy to have as a friend. She is complex and realistic. Flawless in her flawedness. A pony that sometimes errs, but will always go to great lengths to make up for it.