it depends what dragon u want if you want one you can handle all the time etc go beardie prob be better for that size tank
if you want water dragons it prob last for one year max as they are very large dragons but my favourite
tank costs you need
efficient uvb lights (both dragons)
heat lamps (both)
large swimming area(water dragons) need high humidity
ceramic heat emitter(bearded dragons)
bearded dragons need a dry enclosure as they are desert dragons
water dragons need a very large enclosure mine is too small for my three dragons that why they are going outside next summer