Plug Wires

Rule of thumb is the less resistance in the wire the better it will be for performance. Though getting the lowest resistance isn't a mandatory thing, it helps.
Also, thickness helps. You'll not need more than 8mm. Factory is 7mm I think and it is plenty for the task at hand in most cases.
I myself allways cut my own wires to length and route them how I like them to be. Purchaseing cutom length sets is a normal thing for me. A good crimper is needed for good results. I happen to have a MSD crimper.

A nice sunny day, a cold beer/coke or coffee and I'll just take my time routing them.