So far I haven't joined anyone. I have figured that once I join a side it can't be changed, so I have stayed neutral to get a better feel of who to join. It seems the game playes fine by staying neutral, but on the other hand I have no idea of what advantages I can have by joining the Federation or the Rebellion, what are the advantages?

I was told by someone that in order to buy Hjerim I have to join one or the other and complete their main quest line. Is this true?

Another question I have is: what is the best home to own in Skyrim?

You can buy Hjerim once you finish the CW on either side. Aside from that the only thing that changes for both sides is different jarls and some small dialog differences. No actual advantages in either side. Both sides mirror each other in quest.

As for the best home, that really depends on your personal preferences.

Actually, that's not quite true. There is an opportunity to switch sides a couple quests into the CW quest line.

I find it behooves me to stay neutral. The reason being that I can sell my armor/weapons at either Stormcloak or Imperial Camps, scattered about Skyrim