actually, the simple past is not used as often as one may think.
Which tense to use depends on the situation and context. If you just want a short sentence with no links to other sentences or information, then both tenses are fine usually.
However, there are differences between morning, day and year.
--> I have been sleeping the whole morning.
--> I slept the whole morning.
Both ok, first version is better though.
--> I have been working all day.
--> I worked all day.
Please use past continuous. Simple past makes it sound as if you refer to a former job that you are no longer doing.
--> " I have been studying all year."
--> "I studied all year."
Again, please use the first version.
The simple past generally refers to actions in the past that have no relevance to the present time.
The simple present is also used when a one-time actions takes place during a continuous action.
--> "I was on the way home when it began to rain."