|Click on my name above and read my "how-to" guide on "adding a second router".|
If your two LAN's are on different subnets and you wan to keep them that way, you'll want to use the "LAN port to WAN port" scenario.
If there's no reason to separate them on different subnets then the simple solution is to use the "LAN port to LAN port" scenario and put them on the same subnet. If they're already using the same subnet, then the LAN to LAN scenario is still the way to go.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.