It is complicated because their is choice and no absolute answers.
AIM balance omega three and six and ensure you get some long chain omega threes. To do this you will have to label watch and check food contents until you get the gist.
The body can make all fats except the mother omega three and six. Lots of things can block the process including age, so that would be an argument for ensuring a mix.
There are no absolutes. Please discuss dietary change with your doctor.
Within sensible limits less is more but there are different views.
Variety is good as different things contain different fat balances - so a little saturate is ok eg butter coconut small amounts lean meat if you are not vegitarian etc. but scrapings not lashings.
Olive is low in six high in nine and even lower in three. It also has other beneficial things apart from the "lipids" (Fats)
Flax has high three some six some nine. This has a small chart of common high oil sources and a breakdown of contents.
http://www.benbest.com/health/essfat.html
But please see posts on flax as much discussion. Whole food sources have as far as possible to be the best starting point.
UDOs has a good reputation and a useful mix.
RB