Haha Im honestly not the best person to be answering but I always give my best shot!
Species:
D. pulcher = wide bar dat = Siamese tiger = ST - This fish will cost you big $$$ and is rare now. Get the largest, but again over 15" in the aquarium is very rare. Water params: the closer to neautral the better, but as long as it is consistent between 6-8 there should be no problem.
D microlepis = Indonesian dat = Indo = IT - This fish is probably the most common as many many small (around 1") have been imported recently. Care is very similar to ST, infact until the last few years D. pulcher was considered the same as D. microlepis.
D. undecimradiatus = Thin bar dat = NTT - Thin bars I have read to be the least hardy. Otherwise care is the same. They are smaller then previous two.
D. polota = Silver tiger = American tiger = AT - Silvers are probably the cheapest dat. They tolerate fresh and slight brackish conditions. Water should have a pH a bit more on the akaline side. ATs also are on the smaller side, perhaps 12" tops in the home aquarium.
D. campbelli = New Guinea Tiger = NGT - Care for NGT is similiar to AT as they also can tolerate slight brackish conditions though like the AT not 100% required. NGTs tend to be the most aggressive of the dats. Max size for NGTs should be around 14".
Hope this helps, but I dont have enough experience to say the info is 100%.