You should think about this carefully for every subject.
There can be huge competitiveness differences between singular and plural, also huge meaning differences, and huge differences in the frequency of use.
"Coffee" is most commonly used for the caffeine drink. "Coffees" is rarely used.
"Skis" is always used with you are buying a pair. But "ski" is used as a verb or an adjective ("ski boots").
"Diamonds" and "diamond" are very complex keywords. "Diamond" is the word used for the hard material. "Diamonds" is the word used for more than one of the gem. The search results for a word like "Diamond" will have contamination by brand names of companies that make storage devices, pet food, chain, cabinets, archery equipment and more (in this example the competition is so gemstone heavy that gemstones take the first page of the SERPs but brands dominate the second SERP.)
Last edited by EGOL; Dec 8th, 2012 at 11:09 AM.
* "It's not the size of the dog in the fight that matters, it's the size of the fight in the dog." Mark Twain
* "Free advice isn't worth much. Cheap advice is worth even less." EGOL