I didn't like either, but most people seem to like Vivi Nova more. Here's some pros/cons that I can think of, based on me trying both for about a month each and deciding against both.
Vivi Nova
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*Pros:
very easy to add
juice
cheap replaceable heads (same as cartos, really)
doesn't seem to leak
great flavor
heads can be rebuilt to produce better than stock effect, for close to free
Can get metal tanks. More juice resistant, but can't see the liquid level in them
* Cons:
The heads that I got didn't have resistance listed on them, not even close. Like the 1.8 head actually measured at 3 ohm. I assume other people have better luck with them
I also didn't have any good luck rebuilding them -- my rebuilds would either flood, or burn the rubber gaskets, producing the most disgusting smell and taste. Strong enough to where I still tasted it next morning after brushing my teeth with uber mint toothpaste
One of the two Novas I had had the center post slightly crooked, causing it not to seal very well in top. So it leaked a little bit.
To my knowledge, the clear plastic tank can be damaged by cinnamon and citrus juices.
Carto tanks:
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*Pros:
Come in all kinds of purdy shapes, and colors
Come in all kinds of prices
Cheap replaceable cartos (comparable to Vivi Nova)
Most don't leak
If you like cartos to begin with, they taste just like whatever carto you put inside
Some of the nicer ones are immune to all juices.
*Cons:
Can be painful to refill
Some can be slidey. As in, the tank full of juice comes off of the carto and dumps the juice in your pocket
Some can be tight. As in, you have to pull really hard trying to refill it, and the whole thing goes flying, spraying juice on your keyboard
In my experience, the continuous heating/cooling of the liquid surrounding the carto would change the taste of the liquid. Not a problem with some liquids.
Some liquids can cause some of the tanks to deteriorate and start leaking. Cinnamon and acidy (citrus for example) liquids do that.
Edit: forgot to add that some cartos come with no holes. Then you have to mess with punching or slotting them. Some cartos come with holes in them. You'll need to find the right size/number of holes for your juice: if there are too few holes or your juice is thick, you'll get dry hits; if there are too many or your juice is thin, you'll get leaks from the connection side and gurgling.
I would definitely recommend trying both to see if you like either. As far as tanks, I really liked the locking "artemas" tank from discountvapers (it's available from other vendors too). That solved the slidey and too tight problem. A lot of people like the tanks from IBtanked. I don't have those, so can't say anything about them.