I think "Beelzebumon" is actually Japanese translated name.
And Magnadramon/Holydramon and Hisyaryumon are tied for my favorites (Well, simply because dragons).
Yeah, I know. Graizen spelled it "Beelzebuumon".
On the whole, I prefer the Japanese names, generally because they make more sense.
"Diaboromon" is a corruption of "Diablomon"
"Vamdemon" became "Myotismon", which is clever (Myotis is a genus of bats), but... you know, who knows what "Myotis" means?
(that's the point, it was censorship)
"Tailmon" became "Gatomon", when "Gato" is the Spanish word for "(Male) Cat" (Tailmon is female).
"Protomon/Plotmon" (Tailmon's prevo) became "Salamon", named after the translator's cat.
"Omegamon" became "Omnimon", not bad on it's own, but then Omegamon loses it's obvious connection to Alphamon.
"Demon" became "Creepymon", which
everyone (even the dub writers) hates, but Bandai insists on for some reason.
"Lilithmon" became "Laylamon", which is just... ugh... (fortunately this is restricted solely to Digimon Fusion)