I believe destruction is the preferred spec if you want to go for burst damage. The downside, however, is that you lose a lot of mobility, and rely heavily on having a team backing you up. If you want to negate these downsides, at the cost of some of the burst damage, you can try demonology, which offers some interesting abilities and improves your mobility a lot. I've seen demonology warlocks fare well against melee teams, and even as flag cappers. Some unique jumps that are otherwise inaccessible also open up.