There is no simple answer for your question. The main thing is about what you want to do with your data? And do you need so much data at one time?
EF translated your Queries to SQL so at this time there is no Object in Memory. When you get the data, then the selected records are in memory. If you are selecting a large amount of large objects then it can be a performance killer if you need to manipulate them all.
If you don't need to manipulate them all you can disable change tracking and enable it later for single objects you need to manipulate.
So you see it depends on your type of application.
If you need to manipulate a mass of data efficient, then don't use a OR-Mapper!
Otherwise EF is fine, but consider how many objects you really need at one time and what you want to do with them.
