By your question, it is clear that you are planning to invest in Digital ads to bring new customers for your startup.
Whether Facebook ads or Google ads is a better choice for your startup depends on nature of your startup.
Let me clarify what I mean.
While there are many factors that determine nature of a startup, for simplicity sake we will discuss about 1—Mass appeal of your product/service.
If people are already aware of kind of products/services your business offer, they will be searching it on Google to find the best provider in locality.
For example, wedding photographer in your city, electrician in your city etc.
In this scenario Google ads is good fit because your can directly reach people when they are searching for a related business.
For business where people are already aware, Google ads is a better choice.
Now lets take another example where people are unaware if they have a problem and are not looking for a specific product/service.
For example, a children newspaper focused on children friendly news. A newspaper which doesn’t cover violance and crime news and only publish child safe news.
While people may need this kind of newspaper for their children, but they may not be aware of its existence. Thus they may not be looking for such newspaper on Google and makes Google search ads less effective.
In this scenario, Facebook ads will perform better. Because with Facebook advertising, you can target people based on their interest like child safety, children upbringing, parenting etc.
Hope this simple comparison clarifies that suitability of Facebook ads or Google ads depends on nature of business.
There are a number of other factors that are critical is deciding whether you should go for Facebook ads or Google ads as a startup.
And rather than guess work you should directly consult with a Facebook ads and Google ads expert Facebook Ads & Google Ads Consultant who knows strength and weaknesses of both the platform and can guide on what works best for you.