Here are the pros and cons.
Boomburst
Pros:
• Very strong attack to use against anything that resists your STABs.
• If you are using a choice item, it's always safe to use Boomburst since it is your most powerful move and it hits for neutral damage to a lot of Pokemon.
• Only resisted by Steel, Rock, and Ghosts.
Cons:
• It isn't super effective against anything.
Dark Pulse
Pros:
• Better type coverage than Boom Burst.
• Nothing is immune to it.
Cons:
• With Super-Effective damage, it's base power is 160 and is only 20 points more powerful than Boomburst.
• It's inferior to Boomburst in every way unless it gets Super Effective damage.
Overall, I think you should use Boomburst.