What's the best birth control pill that will not decrease libido or cause weight gain?

Most are good. The triphasic types seem to have the least adverse effects and are as efficacious.
IUD/Implant. Regardless of your age, blood pressure, family history, or reactions to other birth control, the most effective and safest methods of birth control are long-acting progestin-only methods, such as the implant or the hormonal IUD. Hormone amounts are low and won't affect libido. They're safe, reversible, and don't affect weight gain/mood. They're almost as good as getting sterilized.