Both are very important "experience and skills".Also don't deny your motivation, how to exploit it.Practise is necessary and you should mention your plan for the future
Although skills and experience should be mentioned in short, your motivation is the most important in the cover letter.2nd in importance is the proper use of language. Experience comes in only as3rd (or later) because skills and experience can be found in detail in the CV.
Both experience as well as skills are important; but stress should be laid on your differential advantage over other candidates and why you are more suitable for the job than the other candidates, that should be more highlighted in your cover letter.
cover letter is the one which shows your skills and experience both. it one which is first attracted by any employer and after that only your skills or experience is being tested..