As a Slovak / Czech speaker I find Slovio a bit easier to understand than Interslavic, despite the mentioned non-slavic choices.
Interslavic seems to be south-slavic biased.
Purely subjectively, Slovio text reads more aesthetically pleasing. I think this might be because the south-slavic roots are more prominent in our east dialects spoken in the country side, while Slovio seems closer to me to the standard codified language.