well, it depends on what you want to do
if you want just a basic display, echo is enough
printf allows you to display with formatting features. If you're
familiar with c, it's similar to c's printf
I'll give you some examples

# i=5

1. echo
# echo $i
5
#

2. printf
# printf $i
5#printf "$i\n"
5
#

# printf "%02d\n" $i
05
#

As you must have noticed with printf the
newline character '\n' is not automatically added as in
echo