As a speaker of Croatian (southern Slavic) and Ukrainian (western Slavic), both Slavio and InterSlavic are bad from the Croatian POW, but InterSlavic is definitely a better choice in either case.
Many word forms in InterSlavic just seem like strangely archaic versions of Croatian, but might pass as "just strange" for Ukrainian.
Many word forms in InterSlavic just seem like strangely archaic versions of Croatian, but might pass as "just strange" for Ukrainian.