IPTables

I need to optimize my IPTable filtering rules.

Please suggest whether the rule

iptables -t nat -A PREROUTING -i eth0 -s 172.16.0.0/12 -j DROP

will deal with spoofed packets better than

iptables -t filter -A INPUT -i eth0 -s 172.16.0.0/12-j DROP

Also, are these rules necessary when I have already enabled rp_filter at kernel level?

TIA

Prakash