I'm travelling to Los Angeles for the first time by myself to visit friends. I would just like to know at immigration will they get suspicious if I say that I'm staying with friends rather than a hotel to save money.
Many visitors stay with their friends; this is no reason for concern. If you are staying with your friend, be sure that you have his or her address, as you might be asked for it.
If the officer really does have any suspicion, he or she may ask your friends' phone numbers and give them a call, but it is not likely.
For me the key things is not with who or where you are staying, but convincing the authorities that you will go home as intended after you finish your visit.
The CBP has no knowledge of what you do once they let you in, and no ability to trace your movements, so they only get one shot at determining how likely you are to over-stay. Thus if you can convince them on entry that you will leave as intended (and that you will be doing nothing illegal!) then there should be no issue with getting in. Such proof would included being honest about where you are going, what you will do, how long it will take, as well as supplying information about homes/job/school/family back in your home country.
Just be honest with the CBP officer that interviews you at immigration and answer their questions as asked. But don't tell them things that they don't ask for or don't need to answer their questions. They know what they are doing and know what they want to know.
Other than that .. enjoy