I'd say you can't do either.
I'll explain. These Ryu are part of the so-called "X-Kan's", so named because the three primary organisations all end in "Kan" (Bujinkan, Genbukan, Jinenkan), and are not taught separately. You may, if in the Genbukan, have the option to train in one specific one after you reach 3rd Dan, the Jinenkan will also introduce you to Ryu-ha specific approaches after Dan grade level, and the Bujinkan will pretty much never give you the option unless a particular teacher decides to offer it.
Additionally, it's not really an easy thing to describe the differences between the Ryu without a more physical education, as it's more in the "feel" of the separate Ryu rather than anything else. I mean, I could tell you that Shinden Fudo Ryu Jutaijutsu has a similar feel to Kukishinden Ryu Dakentaijutsu, with both featuring heavy throws and gross-motor limb controls, but they're still distinctly different... and Shinden Fudo Ryu Dakentaijutsu is a different animal again, but all of that's beside the point as you seem to have no point of reference at the moment.
