i have been doing parli now for two years, and the major problem i see with parli is the lack of warrants that exist in this form of debate. its extremely hard to have an actual debate over a policy when you cant read evidence to prove something to be true, and usually when people give you those warrants they are usually really bad. the idea of "no prep time" also are really annoying, and i think this means parli isnt as educational. just having the 7 or 8 minutes of the speech before you to think of good arguments with good warrants isnt really enough time to think of multiple good arguments without cards.
i also think that if the round isnt policy based, and is fact based or value based it invites judge intervention. for example, a value type round usually makes a judge interject their own beliefs into their decision. if the judge prep-round believes utilitarianism, for example, is good then they are going to pref that side of the resolution.
overall, i personally prefer any type of evidence based debate.