Either method will work, Migration Assistant in the Utility folder, or coping the catalog and photos.
Migration Assistant either needs a Firewire cable between the two machines or an external disk. The newer Macs Power Books only have a Firewire 800 port and the older ones have a Firewire 400, so you need an adapter or use the external hard disk.
If you are migrating Photoshop, remember to Deactivate PS from the HELP menu before you decommission the old Mac, otherwise it eats up one of the two activations you are allowed.
LR does not use activation so that isn't a problem.