I use both fingerings, depending on what's going on. Normally (a la classic guitar) I use the 2-3-4 fingering. Easy transition to and from C, or, say, a progression of G-G7-C, or almost anything within the keys of C and G. Sometimes in the key of D, I'll use the 1-2-3 fingering. If I'm going from G to a Bm, for example, I'll probably use 1-2-3. Just flop the first string down on the 2nd fret (barre) where it already is and put the rest of the fingers where they need to be.

No law sez you have to use only one fingering.

Don Firth