I think that primarily depends on what your budget is and what you are comfortable investing.
Multi-family can be a great way to diversify. By that I mean rarely will all the units be vacant so a little money will be coming in. Whereas when a tenant moves out of an SFR then there is no income till you find another tenant.
In my opinion an SFR can be easier to acquire in this area and if you have never invested before it is a great way to toe dip. And you can always work your way up to multi-family. Or you could consider a duplex, again depending on how much you plan to invest.
Traditionally SFR's will be "cheaper" than a multi family. My ultimate goal is to work my way up to 3 SFR's and then work on acquiring an apartment building.
I know some of this may seem like common sense. But I am not sure what you know and don’t know. So I mean no offense. We can dig deeper if you want.
If I was in your shoes I would first work out a goal. Which it sounds like you want this to set you up for your retirement.
The next step is to decide how much you need to make a month in retirement to maintain a lifestyle you are comfortable with.
Then use what you have now to launch a strategy to work towards the end goal within the timeframe you would like.