A series is easier to wire but depends on all of the parts working. Wiring in parallel is more difficult but if a bulb burns out, it doesn't affect the others.
Work Step by Step
Advantages: Series: the bulbs are easier to wire in series; one wire is run from bulb to bulb. It’s easy to make a cheap blinker bulb to have the entire string flash on and off. Parallel: If a bulb burns out, it doesn’t affect the rest of the string. It’s easy to tell which one went bad. Disadvantages: Series: when a bulb burns out, the rest of the bulbs don’t light. Finding the burned-out bulb is a pain. Parallel: wiring bulbs in parallel is (slightly) more difficult; More wire is involved, and there are more connections and branches.