The answer is: "it depends"!
Here is a good article to read.
But to attempt to summarise..in VERY broad terms:
(always) give 1st preference to "static";
consider "float" to achieve desired layout or, for example, to float images within a larger textual-area;
then "relative", but mainly to supply a content for "absolute" and other positioned elements;
avoid "absolute" but, if used, tend to do so in the context of another (relatively) positioned element;
"fixed" is used rarely, but occasionally is used to fix a small element at one side of the browser window.
Specific layouts are mainly achieved using floats, but some layouts can also be achieved with a combination of relative and absolute positioning. Percentage and/or fixed widths on elements are also used to achieve a desired layout and behaviour. cf
liquid layouts.
People sometimes resort to positioning of elements when they haven't fully explored the use of margins and padding to
separate elements.
And avoid
DIVITIS!
I may have confused rather than helped?? but the links are good
