When choosing which niche to enter for your PLR ebooks you should treat it as you would any other internet business model, the same rules apply to plr ebooks as with google adsense, clickbank or what ever other income steam that you are involved with.
Firstly you should ensure that there is a demand for your PLR ebooks, are people searching for the type of plr ebooks that you are looking at promoting?
When you have satisfied yourself that these plr ebooks would be in demand you should then search for a domain name which includes a highly searched for term which will then be the title for this particular one of your plr ebooks. The reason for this is that it will give you a head start in the search engines and when this domain name is place on the sales page of your plr ebooks it will give a good first impression to the visitor who wishes to purchase one of your plr ebooks.
You will then be supplying your plr ebooks to a hungry market and this means that most of the hard work has already been done, Your plr ebooks will meet a need and you will find that by marketing your PLR ebooks in this way you will have far more success in your plr ebooks business.
When your plr ebooks are successful in a particular niche you should be looking for more plr ebooks in the same niche to offer your customers in the future.