In summary maybe:

1. variables qty

2. experiment's cost

3. process'sl sensitivity

4. resources' avalibulty

5. Researcher's and team expertise

Taguchi for:

Large no of variables, smaller number of experiments, resource is limited & less statistical knowledge os required

Full factorial for:

Highly sensitive

Dear Zatul Faqihah,

1. At first, you should consider parameters affect on coating.

2. Determine number, range and type of parameters (continuous or non-continuous parameters).

3. Exactly calculate the time and the cost required for doing of full factorial design.

4. Compare the time and cost of experiments with availability of your resources (time, financial, materials, etc).

5. Now it is easy to make a decision.