Definitely non-rhyming! Parents aren't being clever by coming up with names like Lily and Millie or Victor and Victoria. Those pairings are far too obvious, and what's worse, they cause people to view your twins as a set rather than as individuals. Twins naturally have identity issues -- help them as much as you can by giving them distinctive names.
If you want to be clever, pick names that are connected in some more subtle way.
Hunter and Jackson work perfectly together. They're trendy, two-syllable boys' names, one with an occupational feel and one with a surnamey feel. They definitely coordinate, but they're distinct in sound.
Hayden Everett and Rosaline Emily work well, too. Hayden and Rosaline are connected in the fact that they both end in the N sound, but they don't rhyme and they have differing numbers of syllables. I like the fact that these parents saved the matching initials for the middle names.
Adalyne and Madalyne are far too similar. However, I think something like Madelyn and Gwendolyn would be okay, as the names don't truly rhyme and the nicknames wouldn't rhyme (Maddie and Gwen).
Ways I like twins' names to "match":
-- overall feel (Henry and Eliza; Clara and Eleanor)
-- ending sounds (Clara and Susanna; Henry and Wesley)
-- language of origin (Greta and Liesl; Kenneth and Malcolm)
-- number of syllables (Caroline and Adelaide; Jude and Rose)
-- beginning letters that make DIFFERENT sounds (Charlotte and Celia; Anna and Audrey)
-- meaning (Eloise and Cyrus mean "sun"; Hazel and Willow are trees)
Very interesting question!