Allah tells us laylat ul Qadr is worth more than 1000 months of worship. So that is the best night, and the best nights are the last 10 nights of Ramadan. But the best 10 days are the first 10 days of Dhul hijjah as it contains the day of Arafat.
If you have not gone for Hajj it is sunnah to fast on the 9th of dhul Hijjah. Fasting for this day expiates the minor sins committed for the year before Allah loves the good deeds during these days so much he gives us forgiveness for fasting.
How merciful is Allah, He (swt) gives us blessed days and months to gain his forgiveness. Allah is reminding us that whatever we have done Allah forgives us. We can spend 70 years with shaytaan but by spending one minute with Allah, you can earn his forgiveness.