Should I use live rock or dry rock?

Short answer

Dry rock for new builds (no pests, half the price, 6-8 week cycle). Cured live rock for established hobbyists (faster cycle, instant biodiversity, but higher cost and pest risk). For most beginners, dry rock + bottled bacteria starter is the cleaner choice.

In depth

Live rock used to be the only option. Today the choice between live and dry rock is one of the most consequential early decisions in a saltwater build.

Live rock

Cured live rock: $5-12 per pound. Pre-cycled at the vendor, contains established bacteria, microfauna (copepods, amphipods), and often coralline algae. Cycle takes 2-3 weeks.
Pros: instant biological filtration, biodiversity, established microfauna for coral feeding, attractive coralline coverage
Cons: pest hitchhikers (Aiptasia anemones, vermetid snails, predatory crabs, mantis shrimp), high cost, can re-cycle if exposed to air during shipping

Dry rock

Aquacultured dry/dead rock: $2-5 per pound. Marco Rocks, BRS Reef Saver, Pukani. No biological activity, no pests.
Pros: 50-70% cheaper than live rock, zero pest risk, cleaner aquascape (you can shape it before adding water), no shipping stress on biology
Cons: longer cycle (4-8 weeks vs 2-3), no biodiversity initially, no coralline coverage (will develop over 6-12 months)

The hybrid approach (best of both)

Many experienced reef-keepers use 80% dry rock + 20% live rock. The dry rock provides clean structure; the live rock seeds the system with bacteria, microfauna, and coralline algae spores. Cycle takes 4-5 weeks and you get most of the live-rock biodiversity without the full cost or pest risk.