I proposed marriage to a religious girl, but she is not beautiful. Should I marry her?
Question

I proposed marriage to a girl who is very religious but she is not beautiful, and I want a wife who is more beautiful. What is the right thing to do?.
Praise be to Allah.One of the important reasons for which Islam has prescribed marriage is to achieve chastity and to protect oneself and prevent one from looking at haraam things. In order to achieve that, Islam encourages looking at the fiancée before getting married to her, as that will ensure that love and affection will be generated between them, and will create a happy family, based on love, affection and respect, and neither spouse will be tempted to do something other than that which Allah has permitted. Hence beauty is one of the attributes which one is encouraged to seek and pay attention to. 
It says in Sharh Muntaha al-Iraadaat, which is a Hanbali book (2/621): 
It is also Sunnah to choose a beautiful woman, because it is gives a greater sense of transquillity and is more likely to help him lower his gaze and love her more. Hence Islam prescribes looking (at one's fiancée) before marriage. 
It was narrated that Abu Hurayrah (may Allah be pleased with him) said: It was said: O Messenger of Allah, which of women is best? He said: “The one who, when he looks at her he feels happy, when he tells her to do something she obeys him, and she does not go against his wishes with regard to herself or his wealth.” Narrated by Ahmad (2/251); classed as hasan by al-Albaani in al-Silsilah al-Saheehah (1838). End quote. 
Some scholars regard it as mustahabb, if a man wants to propose marriage to a woman, to start by asking about her beauty first, then about her religious commitment. That is because it is known that people seek beauty first and foremost. 
Imam al-Bahooti said in Sharh Muntaha al-Iraadaat (2/621): 
He should not ask about her religious commitment until he has been told good things about her beauty. Ahmad said: If a man wants to propose marriage to a woman, he should ask about her beauty first, and if good things are said, he should ask about her religious commitment, and if good things are said, he should marry her. If he does not hear good things about her religious commitment, then he will have rejected her because of her religious commitment.  He should not ask about her religious commitment first, then if good things are said, the he asks about her beauty, then if he does not hear anything good, he rejects her because of beauty and not because of religious commitment. End quote. 
What is blameworthy is when a man seeks beauty and forgets about character and religious commitment – which form the foundation of happiness and righteousness. As this is how most people are, the hadeeth urges them to look for one who is religiously committed and of good character, to stop people focussing on outward appearances and ignoring inward qualities. 
It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “Women may be married for four things: their wealth, their lineage, their beauty and their religious commitment. Choose the one who is religiously-committed, may your hands be rubbed with dust (i.e., may you prosper).” Narrated by al-Bukhaari (4802) and Muslim (1466). 
Al-Nawawi said in Sharh Muslim (10/52): 
The correct view concerning the meaning of this hadeeth is that the Prophet (peace and blessings of Allah be upon him) was speaking of what people usually do, which is that they look for these four characteristics, the last of which in their view is religious commitment, but you who are rightly guided should choose the one who is religiously committed. End quote. 
The view that it is mustahabb to seek beauty in one’s intended wife does not mean that dazzling beauty is essential, and that a young man should imagine the image of a girl who is one of the most beautiful women in the world and spend his whole life pursuing the image that he wants, because in most cases he will not find her, she may be weak in religious commitment and character. 
Rather what is meant by beauty is the kind of beauty by means of which a man will keep himself chaste and avoid haraam things, and he will refrain from looking at other women. The definition of that beauty will vary from one person to another, and what matters is the opinion of the one who is proposing marriage. 
Our advice to you is not to propose marriage to any girl unless you know that she is of the level of beauty that you are happy with, so that it will not be a matter of initial keenness after which you get fed up or start looking for something new, which will lead to a difficult series of problems in married life. 
Whatever the case, the matter of religious commitment should take precedence over everything else. 
With this balanced approach and balanced way of thinking, you can build a happy family life, in sha Allah. I ask Allah to help you and decree good for you.  
See also the answer to question no. 8391 and 21510. 
And Allah knows best.