in my opinion a hardtail is much better suited to dirt jumping, that bit of give on a duallie soaks up your pump and that makes it harder to get over the last few jumps on a dj set. also a hardtail lets you know when youve come up short on a gap so you it forces you to learn to be smooth and thats important if you want to hit bigger, less forgiving jumps. a hardtail has way more advantages than a duallie when it comes to dirt jumping. it gives you a more responsive bike, less maintenance, costs less, its lighter, teaches you good dj habits in terms of smoothness/speed judgement, more efficient in tight ramps and generally feels better in the air since it allows for tighter geometry and a lower centre of gravity