I actually have and use both (no real reason - I initially just wanted to try both when they were new and just kept on using them). Either one will work fine and have never failed me. I like SuperDuper's scheduling for incremental updates to the clone better than CCC's, but that is about the only substantial difference to me.
Initially, when Lion came out with the recovery partition, there was an issue with SuperDuper, but the update was pretty prompt to deal with that. I seem to remeber CCC had an update just before the public release of Lion, so Mike B. was a bit ahead on that.
I have SuperDuper set up to clone to a partition on the same drive I keep my TM backup on, and it is scheduled to update that clone once a week. I also keep two portable, bus-powered hard drives for clones (one CCC the other SuperDuper - one offsite, and one kept in home firesafe). They've all been fine and that has been my backup strategy for several years now.
Since you can try both for free, check them out and see which one is to your taste - you really cannot go wrong with either.