First of all, welcome to bitcointalk! That is a good approach, to get yourself familiar with the forum. Take your time, read the rules, there is no need to rush into anything. Newbies tend to do  that mistake and they end u getting banned (pay extra attention to proper referencing when copying an external article). So make sure that you know do's and don'ts. A lot of newbies tend to ignore that part and it doesn't end up well for them.



Regarding your question, in my opinion it's best you write about the stuff that you are interested in, whether it's bitcoin, altcoins or something else. Don't feel pressured writing in some section about stuff that you don't care about as it will affect your post quality, whether you want it or not.

Since you are still new I would advise you to read this guide made by @tranthidung Bitcointalk posting etiquette. It has a lot of useful info and will set you on the right track from the beginning.