Running time of CDCL compared to DPLL
Both CDCL and DPLL need exponential time in the worst case. I am not sure if it can be proved that CDCL is always faster than DPLL on every instance, but there is major empirical data suggesting it dominates. For a nice, short overview see the presentation Boolean Satisfiability Solving: Past, Present &amp; Future by Joao Marques-Silva. He also has quite a few related talks online, see here.

CDCL is the dominating solver among all modern solvers. I would claim CDCL does indeed always dominate, and that is because it's basically a DPLL-based procedure, but with additional enhancements. It uses information gained during the search, restart strategies, special data structures, and so on.

There are instances that make all the known DPLL-like algorithms run in exponential time. For example, Alekhnovich et al. [1] exhibit such a family of 3-SAT instances. For more information on satisfiability, both theoretical and practical, I think one of the best sources are the Handbook of Satisfiability [2] and the regular International Conferences on Theory and Applications of Satisfiability Testing, known as SAT.



[1] Alekhnovich, M., Hirsch, E., and Itykson, D. Exponential lower bounds for the running time of DPLL algorithms on satisfiable formulas. JAR, 35(1-3), 51-72, 2005.

[2] Biere, A., Heule, M., van Maaren, H. and Walsh, T. (Eds.). Handbook of Satisfiability. IOS Press, 2009.