Relative stability of contributing structures:

Rules for Resonance Stability Step 2: Evaluating Structures

• (I) $CH_2=CH-CHO$: Neutral, all atoms have complete octets. Most stable.
• (II) $^+CH_2-CH=C(O^-)H$: Negative charge on Oxygen (electronegative).
• (III) $^-CH_2-CH=C(O^+)H$: Negative charge on Carbon and positive on Oxygen. This is highly unstable as Oxygen is more electronegative than Carbon.

Step 3: Order (I) > (II) > (III).

$\boxed{\text{Answer: (b)}}$