I use Zillow just for supplemental data and cool map features but it is extremely inaccurate.
For instance a property I own is across from a posh neighborhoood with a very highly regarded public school district. The school district of this house however does not belong to it although 1 mile away same city as mine belongs to the school district. This is a 100-200k difference people are willing to pay. Zillow reports it is in the good neighborhood which is wrong. Also I paid 100k below market for this home and now zillow assesesses the value low. I can easily sell this house much more.
Loopnet is garbage. It is the biggest pool for commercial property. But most of these properties are junk no one wants or leftovers from the MLS. Some agents in my neigborhood put their overpriced garbage condo listings in the investment property section. Also Loopnet charges money for you to see some garbage listings. And once you have tried it like I have, they charge you for data such as potential buyer contacts. They also charge if you want records of what sold and if you want to run a CMA. When I sold a house I listed below market value posted on Loopnet, I never heard from 1 buyer. After selling it they wanted to know how much I sold it for. Oh really so they can sell that data which I had to pay for? It sold for 390k I but 5 billion hopefully that skews the data a bit.
They are all junk for investors. Redloc might be useful but they don't update often and fast enough from what I heard. I don't use it.
MLS is good during a market like now but still you get a lot of competition.
LA county assessor is free.
I use realist tax to get property info so I don't have to kiss [censored] to a title rep.