For the small price difference, the Rumble 25 is a good choice. Sounds good at low volume and can be loud enough for your acoustic jams. I’m surprised though that you don’t find the 40 to work for you.
I love the rumble 40 to be honest. But I've not once had the chance to turn it up past about 1 or 2 (if it had numbers) and so it seemed unnecessary to me to have an amp with that kind of power, especially when it's taking up too much space. I'd only replace it with something if it was significantly smaller though and still had some low end. Otherwise I'll just keep it in the corner and get it out once or twice a week as I do now.
Another thing I forgot to mention is the fact the Rumble has that soft vinyl covering on the front which I have to keep away from my son at all times or else he'll destroy it (trust me
