Thinking of taking the Datnoid plunge...good decision.
You could start with ITs...they're probably the cheapest and easiest to maintain considering all that goes into caring for them. My ITs were eating frozen foods the day after I got them. STs are similar, just much harder to find...and much MUCH more money.
My NTTs eat frozen/prepared foods, but they are very shy, so you may notice some wasting if they are in with more aggressive dats like NGTs or ATs.
My ATs are by far the most aggressive out of the bunch. They will attack anything that comes between them and their food. I've lost a few tankmates due to the wrath of my ATs.
My NGTs are pretty shy, but they can dish out the hurt when needed. I've had more of a challenge getting them to eat prepared/frozen foods though, so it may take longer to wean them.
Basically, I would decide what you want out of a dat and then get the species that best fits you. ITs are you "standard" dat, STs are the rarest, NGTs are somewhat rare with added color, NTTs are shy and have a lighter coloration, ATs are unique in that they are the only silver dat, and they also have a higher level of aggression.
What type do you show a preference for??