which house?

How do you feel about the girls you met? Any sorority girl can go to any open party at any frat, so you are at minimal disadvantage socially. The most important thing is how well you click with the girls that you have met. Phi Mu is new but will move up soon, but that should not be important in your decision.

Good news - between those 3 houses, you will meet great girls in any of them, so just join where you like the girls the most.

I'm unsure what you mean by "disadvantage". If you mean people bashing you on a random anonymous website, maybe. If you're joining a sorority for networking with alumni, maybe. Those don't seem like any valid reasons to not join. It's important though to look at who is around you when going back to these houses - they will be your pledge class. Also if living in is important to you, phi mu may also not be the option as only 27 girls can live in. Go with what your heart says.

As for the post above, not many fraternities have open parties. If they do on the rare chance, you do not need to be in a sorority to attend, usually you have to know somebody/where to go. This "rush party" period doesn't last forever. Socially, only phi mu can speak about phi mu. They have had block but that isn't significant as this year it is only three weekends and all sororities usually have block. I'd say it's likely aopi or phi sig would have more social events with similar fraternities, but it's all up to you. Those houses are all great selections if you feel great!

When I was rushing, they told me that they have all the same events as other sororities like formal, barn dance, and stuff like that so really I don't see them any different from the rest

Curious which you went with! Would ask to DM but obviously that doesn't exist. Anyways, just want to know if you're happy!