HGSS is seriously way easier for breeding. I'm am not exaggerating. The cowgirls in DPPt can screw you over for hours and days of RNG, but you can get a perfectly IVed shiny poke in under 2 hours on HGSS.
Catching standing legendaries, I'd say is about equal, but there's more math in DPPt and because of the math, I'd say it's harder. In HGSS, it's just a matter of looking at roamer positions and calling Elm or the radio.