In my experience, D.graomogolensis and D.spiralis are the easiest. Both should be good starter species. D.tomentosa, D.tentaculata, D.felix, D.kaiteurensis and D.latifolia are also fairly easy assuming that you have the proper conditions for them. Avoid starting with species like D.villosa, D.meristocaulis, D.camporupestris, D.solaris, D.roraimae etc... They're much pickier and less forgiving than some of the others