AS path length

All AS vs. unique AS count:
Prepending - repeating of AS 
Makes AS path look longer
Reduces traffic via this path
Bumps at AS path length 12,14 
e.g., 202.183.247.0/24  3561 5400 5400 5727 4651 7568 7568 7568 7568 7568
5 unique + 5 repeated ASes == AS path length 10

Routes are chosen by Local Preference 
Other metrics: 
Multiexit discriminator (MED)
Communities 
but
AS path length is used as default metric