Why not do both, depending on the song? The student won't stress about cross harp vs straight if you don't. I like the MM's a lot for celtic music myself. Some examples playing O'Carolan -- Shebeg Shemore (sp)? lays out fine straight harp, as does Planxty Irwin. Fanny Power has too wide of an octave range for standard tuning, but sounds good on a melody maker. Ashokan Farewell is another natural for this tuning. I use the notation layout chart on the Lee Oskar website as a guide to write tab. The MM's play straight harp in a minor key, which is another fun thing to play around with. The big disadvantage of MMs is that chords sound terrible because of the altered notes. For this reason, I would start with standard tuning until single notes sound good.
I have a new pupil,keen to learn irish music,the instrument i play well is the standard diatonic blues harp. however there is always a note missing down the bottom end,the melody maker has this note,should Iteach the pupil to play straight harp[on the instrument i am familiar with]the 10 note blues harp,or the more versatile melodymaker[which i am not so familiar with[melody maker stars on suck2instead of blow4]any opinions.www.dickmiles.com