Hi Anish, I'm a real estate agent specializing in the investment properties for South Bay / Silicon Valley / Santa Clara County area and I can answer your answer for that region.
Investment properties are a very big segment. You can roughly divide into A) apartment complex of 5 units or more B) multi-family dwelling units of 2-4 units and C) single family units such as houses and condos. Based on your investment objective, risk tolerance and capital available for investment, you usually will focus on one segment. For example, you have up to $500K for investment, C) is the only available option. If you have $500K to $1M, B) may be a better option. Then cap rate depends on rent, HOA , property tax, insurance, management fee. It varies from property to property. You won't make the best investment decision if you generalize at a city level.
In the South Bay, from my analysis, you will get the best cap rate in Sunnyvale, Santa Clara and San Jose. If you pick the right properties, you can get as much as 9% cap rate. The operative word is "right". We have all the analysis tools to consolidate all the data and recommend the best opportunity for you. If you are interested in rental properties in those areas, please contact me.