If you had to choose only one of these three, which of these "lovestyles" makes the most sense from a biological perspective?
polyandry - love for many men. The woman has more than one husband.
polygyny - love for many women. The man has more than one wife.
polyamory - love for many. Many loves for either gender.
The biological perspective needs to be taken in view of the sociological context. If you are just talking about pure biology, in reference to procreating, then they all would serve some purpose. But it is meaningless without looking at the sociological ramifications.
"I love the man that can smile in trouble, that can gather strength from distress, and grow brave by reflection. 'Tis the business of little minds to shrink, but he whose heart is firm, and whose conscience approves his conduct, will pursue his principles unto death. " Thomas Paine