ip is faster and have more configuration options, so your choice should be ip.
time ifconfig -a >/dev/null
real 0m0.010s
user 0m0.001s
sys 0m0.008s
time ip addr show >/dev/null
real 0m0.004s
user 0m0.000s
sys 0m0.002s
ip is faster and have more configuration options, so your choice should be ip.
time ifconfig -a >/dev/null
real 0m0.010s
user 0m0.001s
sys 0m0.008s
time ip addr show >/dev/null
real 0m0.004s
user 0m0.000s
sys 0m0.002s