Both blog and vlog are meant to share the experience of a person about the things he has used, bought, performed activities or anything for which experience can be shared. Blog express these feelings or experience using written language while vlog documents all these using spoken words and video.

Vlog involve speaking about something as you are using the product, performing the activity or unboxing the new bought item, so vlog usually contains your instant feelings and thoughts.

On contrary, blogs are usually written after activity is complete or end of the day of end of the tour if you have travelled anywhere. So it is more about recollecting your memory about what you felt during that particular course of time. So it is only after completion and writer have enough time to thought about it and have ample of words to express. While in vlog, speaker usually missed on some of the best vocabulary that is required.

Blog is well planned and well written while vlog can be well planned but well execution is difficult.

"Writing makes a man perfect" this proverb is well established.
Blog vs Vlog