USB 3 would be fine except your old MBP only has USB 2.
And your MBP is only a Core2 Duo so on the underpowered side anyhow. And you have a Firewire interface, so you've got a kind of crapshoot here. Firewire 800 disk will work better on a Mac than USB 2. But you are then putting a Firewire disk and interface on the same Firewire chain, and face possible problem with that.
Still I'd go with a proper-spec Firewire 800 drive (7,200 rpm or faster and Oxford Firewire chipset)... You may also have the option of replacing the optical drive in your MBP with a 2.5" SATA HDD or SSD (get a Samsung 840 Evo or Pro). Or even better get a new MBP
And as always, a good SSD would be better than any HDD, especially if going internal and your optical bay has a SATA III connection (I'll check later...).
EDIT: Nope looks like the Superdrive in this old girl is PATA so an internal drive is a non-starter.