What you are actually looking for here is dynamic headroom in these small practise amps... Most of them like the original microcube, breaks up very easily at medium volume. What this means is that the small speaker found in these amps can't really handle the power and starts distorting badly.. This ruins the tone of the amp.. The original microcube can only sound good with the volume below halfway..

Unless you are planning to play at very low volumes or through a headphone, you need a bigger amp with at least an 8 inch speaker. Btw, the microcube rx however, sounds a lot better, punchier and louder.. But at double the price of the original cube, not really worth it if you ask me.. Modeling amps rated at 15 watts above like Cube15, Vox VT and Line6 Spider series should do the trick..