Albert Einstein said "“Men marry women with the hope they will never change. Women marry men with the hope they will change. Invariably they are both disappointed.” 🙂
They also say that a woman should marry a man who loves her more than she loves him.
I'd say marry only for love – either the instant spark that sets your soul on fire kind or the slowly growing flame kind that keeps you warm inside kind. But marry ONLY when you are both in love.
To further explain my answer – I don't know if you are comparing the loves or if you are saying its completely one sided. So I'll cover both aspects:
Obviously if its a love marriage, the love will be mutual. Who loves more and who loves less wouldn't, and shouldn't, matter. For no two people ever EVER love the same way and there is no bigger insult to the emotion than to measure it and compare it in any way. You should both want to marry not because you can live with each other, but because you cant live without. Simple.
However, if one has to "choose" a life partner, like in an arranged marriage setup, your question becomes pertinent. But I'd say its relevant only in the beginning – and you should make sure of that. Let me ask you this – why cant the one who loves you be the one you love? Isn't his/her love for you invitation enough? If someone loves you despite knowing or sensing you don't love them equally that much, and if that someone continues to love you nevertheless, wouldn't you eventually fall in love with them as well?
"Eventually" is the keyword here. No one – man or woman- should marry someone they don't love. Or someone they believe or know they can't love, if we are being conservative about the time you have to invest in the relationship. However, just because you don't reciprocate someone's feelings at the outset, don't discredit the potential of eventually being happy together. Marriage is a mature decision and mature love is not just about the butterflies in the stomach or the gifts and grand displays of affection or raging hormones. Mature love is about mutual respect, patience, seeing a better person in your partner, belief in their character and hence faith that together you can and will weather all storms.
So if someone you don't love loves you and wants to marry you, tell them you need time and try to allow yourself to love them. I'd say you are lucky to have them, give it your best and genuinely see if you can get to know them better and love them for who they are and how they treat you.
Of course, you can't force yourself to love someone but, as Rumi says, you can and must seek and remove all barriers within yourself that you have built against love. Only then will you make the right decision and only then will you be at peace with it.