Personally, I just go by what Viz has printed. That is: Ryoga, Jusenkyo,
Nanniichuan, etc. It's not really true to the original Japanese/Chinese (i.e.,
Ryoga should really be Ryouga), but it gives me a frame of reference to
maintain internal consistency.
Understandably, many people hate Viz's semi-accurate translations (like "Mr.
Soichiro"... bleah), but they're the ones what prints 'em, so it seems as
close to "canon" as we can get without writing in Kanji, as Mr. Kleppe suggested.
Someone else will no doubt say "DO NOT use the Viz translations!!" but that's
the beauty of so many diverse personalities, right? :-)