Conduction or convection — which vaporizer should I buy first?

Conduction first, for most people. Conduction units (heated chamber walls) are cheaper, simpler, quicker to learn, and deliver reliable session-style vapor — everything a first device should be. Convection (heated air, on-demand draws) is the flavor-and-efficiency upgrade: buy it when you can name the specific thing your conduction unit does that annoys you — cooked-tasting ends of bowls, wasted half-sessions — rather than because a forum told you to skip ahead. The honest parallel to flower tiers holds: convection is the refinement lane, and refinement is worth paying for once you know you want it.