Source: was an athletic vegan for a long time.
1. I use "Garden of Life B12 Vitamin - mykind Organic Whole Food B-12 for Metabolism and Energy, Raspberry, 2oz Liquid". I went from B12 deficient to B12 adequate on blood tests, so it works (for me).
It's also worth pointing out that I eat a lot of nutritional yeast, and it was not covering my B12 needs at all. AT ALL.
Contrary to Wikipedia and popular belief, B12 producing bacteria has been found in human small intestines (https://www.ncbi.nlm.nih.gov/pubmed/7354869). It's just not clear why it lives in some people and not in others. Prior to modern hygiene practices vegetarian humans and animals probably got it from ingesting feces (in contaminated water or food fertilized with feces).