1 NIC with 2 IP addresses

Anyone please tell me the difference in using 1 NIC with 2 IP addresses (different subnet) and 2 NIC with 2 IP address (different subnet).

you can have 1 NIC with 2 IP addresses by using alternate configuration and setting another static IP address to the NIC, and when the first default static IP address times out, the next one kicks in.

2 NIC with 2 IP addresses....i didn't quite understand what you meant by this, as 2 NIC with 2 IP addresses is a usual condition whether it is on the same subnet or different

2 NIC with 2 IP addresses in one machine and 1 NIC with 2 IP addresses in one machine, both in different subnets.

Which method is best to use? and what is difference between them?

ideally 1 nic with two IP addresses should be ok but depends on what kind of requirements you have.
2 nics on the same pc, might have some configuration issues to be dealt with when times comes to perform effective routing if that pc is also acting as a router or has a router connected to it. people have had many issues or so much as to say "problems" with IRQ conflicts on the two network cards. but if you can make your way around those conflicts and other issues, this method can used as well.
but ideally one pc with 1 nic and two static IP addresses should be a good combination as you dont need to worry about most issues faced by the other combination.

Thanks Arani.