Have squirrels getting into the attic and looking into getting my first air gun. Leaning towards the Benjamin Marauderm as I want something made in the USA.

Would like it to be as "backyard friendly" as possible, but also as powerful as possible in regards to killing squirrels.

Should I definitely go for the .25 or is there a reason the .22 might be better for this situation?

The .22 is plenty adequate for squirrels.  The .25 will have an advantage on shots further away than 75 yards, but that can be considered nearly long range shooting.  The main advantage is wind drift, and a small amount of shot placement forgiveness.

In addition, the .25 is slightly more expensive to shoot, and you have to fill more often. By the way, you probably won't just be shooting squirrels with it.  You are likely to start shooting a lot more.  

Plus, the .22 is a bit quieter than the .25 but both are rather quiet.  The .25 pellet striking stuff does make more sound than the .22s, however, that is a minor thing.

All this said, I personally don't have much use for the .22 and have mostly .177 and .25 airguns.

I have had a MROD 22 for 7 or 8 years. Its accurate, nearly silent and efficient on air. For your quarry it'll be plenty of FPE. I don't see a reason to step up to a 25. Unless you just want one... then rock and roll and smack them with bigger pellets!

Have a .25. It is a squirrel hammer. Drops them in their tra cks.

Thanks. Honestly, I can get the .25 cheaper so I was just curious if there were any big reasons to avoid the .25 over the .22.
I'lll be getting the .25! Thanks for the input

Either caliber will kill a squirrel with no problems.

I agree. I’ve killed plenty with the .177. But larger is a bit more forgiving.