when creating a review site do you think adding the word "top 10" or "best 10" will improve ctr? or do you think it is just better to have the word "Best widget reviews without the top 10?
You cannot label ads that way, it's misleading and usually a violation of most ad networks terms of service.
Do you mean in the title? the description? the text? 'ctr' usually refers to adsense but as this isn't adsense section I gues you mean number clicking on your site in the serps I have a site section of 'top 10...' but I've never seen anyone reaching the pages by searching for 'top 10' anything, so I guess it's an uncommon search term. So as a keyword, I think not valuable. As part of the description, it should catch peoples attention in the serps (page description is often used in the serps) so may be a good idea. If you are talking of adsense, answer as above - you can't use it to label ads.