interesting. From my perspective (Slovenian native, know some Serbo-Croatian & Russian), Slovio is much better.

At first glance:

- Interslavic needlessly complicates the alphabet - there is no need for "y" where "i" would suffice, there is no need for "Ě" where "je" would suffice

- Interslavic needlessly complicates spelling / words - surely there should be a drive towards simplification and shortening, especially in a "shared" langauge:

    "koristajut" -> "koristaju"
    "medžuslovjansky" -> "medslovanski"
    "jest" -> "je" or "es"

In general, I can understand most of Interslavic and most of Slovio, but Slovio is easier.