1 bed rooms vs 2 bed rooms

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I just want someone else's opinion.

I'm looking at 4-plex units in the Saint Louis area. Most people seem to advise "Avoid one bedrooms because they are harder to fill" is this generally advised? It seems you have a better chance of finding 4 plexes that are all one bedroom units or a combination of two 2 bedroom units and two 1 bed room units. It's really rare to find a four plex that has all 2 bed one bath units for all of the units, and if you do it's $,$$$,$$$.¢¢ ok well not that much but you get my point.

Anyone with experience with 1 bedroom units? How do you fill them quick? Or is it just advised to avoid them unless you live in a senior friendly neighborhood?