Polygamy is the exception 4:3

And if you are frightened and anticipate something undesirable because you will not deal justly with the women under your control who have lost their father and have not reached maturity because you will not give them their dowry, then leave them and marry women who seem agreeable to you: two or three or four. But if you are afraid and expect adversity because you will not treat them equally, then be satisfied with one of them, including your own bondswoman. Choose from that which is lawful to you among orphans and wives from one to four, or limit yourself to one, or choose from your right hand possession. That is closest to keeping away from causing hardship.

One wife is best if. Polygamy is an exception and is allowed to remedy specific conditions such as war, shortage of available men, etc. In the U.S. it is the law to have one wife and polygamy in this country invites unnecessary conflict. Because polygamy is an exception, most Muslim men - even those in Muslim countries - have one wife.