Here you are:
1) CrossAdvantage: Examiners can determine CLEARLY where your point is, and whether you can plot
accurately. Especially for points like 3.6, 2.8...
Risk Analysis: The cross can be too small, and escape notice. You have to make it big enough. With a sharp pencil.
2) DotAdvantage:The dot,
if encircled is clearly noticeable.
Risk Analysis: Where is your dot exactly??
Personally, I prefer the cross. It's 'safer'...