Yes, you should use quotation marks, because when you conduct a search without the quotation marks, you get results that contain your keywords in ANY COMBINATION, but if you conduct a search with quotes, you will get results from pages that only contain your EXACT keyword phrase.
This will give you the true idea of how many pages you are competing with for your keywords.
So a keyword like 'cheapest flight to Newyork' might have 700,000 results without quotes, but 40,000 results with quotes.
If you search without quotes, the results which appear might have the keywords that are not necessarily in that particular order or might contain only two words in the keyword phrase.
Have you come up with some keywords yet?
If not then:
Use Google keywords tool (https://adwords.google.com/select/KeywordToolExternal
You should target keywords which have more than 2000 'broad' searches per month AND which have less than 50,000-60,000 'phrase' match results. (use the keyword you get from Google keyword tool and search for the keyword with quotation marks and look at the number of results).
Any keyword with searches below 2000 will not be profitable enough. And any keyword which has results in google above 60000-70000 will be too tough.
It doesn't matter if it is a long tail (more words) or a short tail (less words) keyword. If the particular keyword meets the above criteria, then you should be ok.
But that said, MOST of the short tail keywords are gone now. They do not meet the above criteria. They went like 10 years ago. So you will have to concentrate on long tail keywords.