Possible SPOILERS!

I'm sure many would want to side with the Brotherhood of Steel and believe me, I love the BoS from Fallout 3 as much as any of you all. But I didn't side with them in Fallout 4 because they are lead by a different leader not Elder Lyons, and their purpose seems greedy. Though they give you great amount of weapons and resource. Yes, I know they are doing good for the people in Commonwealth; but going against the Railroad because they are freeing synths? That's has gone too far for me, I couldn't sit back and watch them slaughter the Railroads.

Minutemen aren't bad, though they are only quite a small amount. I like siding with them is because we could be their General, we can build our own base etc. Why not be the leader instead of a follower.

I sided with the Railroad in Fallout 4, though I disliked the Railroad from Fallout 3 because they look stupid and useless. But the Railroad in Fallout 4 is just badass! They have an underground base and their purpose is the same as Fallout 3's, to free the synths. I liked their purpose and their team, they are like the Reilly's Rangers from Fallout 3.

I admire the purpose and base The Institute has, but I couldn't accept the fact that my son is Father. They have these badasses called Courser, which is very hard to kill. I would join them if my son wasn't Father, I couldn't take the truth and refuse to join them. I got the Brotherhood of Steel involved with them, and Father wasn't happy with mom. LOL
We could also be the leader of the Institute, which is quite awesome.