I highly recommend DOA5 now. As the new patch makes it so much easier to unlock everything. Though that might still be hard on the PS3 because I hear from GameFAQs, DOAWorld and FreeStepDodge(top DOA fansite) that the PS3 online scene is all but dead.
Right now, the ZOE HD Collection is a priority one. Konami only does a single print run for their HD collections, because they eventually appear on the PSN Store.
DOA5 is the next title on the list and I can obtain it for about $30 (new) at certain stores now. I don't play online often, but when I do it's with my friends so that's not a problem.