As stated above, synthetics are easier to apply and remove. They are also more durable depending on which brand/technology you go with, but unless it's an actual "sealant" the longevity isn't that much more than a quality carnauba.
Weather conditions and whether the car is garaged or not play the biggest factors in how long a wax will last. For instance, I waxed my mark viii (garage kept & only driven on nice days) with Mother's "pure" carnauba (not their carnauba cleaner wax) at the end of September 2014 and it still beaded very nicely when I put the car up at the end of October of 2015. Although the beading wasn't as good as when first applied, the fact that the paint was still as slick as glass and still beaded water, shows that there was still a level of protection... granted the car only accumulated about 1k miles in that time frame, it's still proof that weather conditions are the biggest factor and carnaubas don't get the credit they deserve in the durability department.
As far as looks go, carnauba waxes give a deeper/warmer look almost as if the paint could melt. Synthetics tend to give you more of a look as if the car was dipped in glass with more of a hard/mirror look sitting on top of the paint. Synthetics are known to make the flakes in a paint job "pop" a little more as well.
A lot of folks seem to prefer synthetics on light colored cars instead of carnaubas... the reason being that they don't benefit as much as dark colored vehicles in the depth department when it comes to carnauba waxes.
I picked up some Mother's CG synthetic wax to try out next spring, I've seen side by side areas on a dark car and it actually darkened the appearance of the paint while adding a crisp shine. By the way, I was extremely happy with their pure carnauba on my opal opalescent.
The Meguiars you mentioned has good reviews, just make sure you clay the car (if needed) prior to polishing or waxing for maximum results. :thumbsup:
