Just like Nout wrote, the singing is very important.
If the vocals don't match with it we change from C to D.
Our fiddle player use two fiddle and I love the lower sound of the C-fiddle
From the songs we play Pillette Breakdown is my favorite two step and Livre de Tabac my favorite waltz on the D-accordion.
I realy don't know if there are typical D or A songs.
Please tell us members from Louisiana ?
Check out some beautiful waltzes played on a D accordion from Jude Moreau's
CD "Retourner au Les Vieux Temps". Valse a Tolan is one of my favorites
and, like several of these tunes they don't sound right on a C accordion.
Jimmy Breaux has a good number of tunes on his CD's that he played with a D. Most of the Savoy-Doucet cd's are predominately done with D accordions to suit Ann's voice.
Two of my all time favorites Eddie LeJeune (any album) and Horace Trahan (on the Ossun Blues album) do a bunch of songs in D. Also Geno Delafose does the Opelousas Waltz which is a great and simple waltz in D (the Amede Ardoin Opelousas Waltz, not the Austin Pitre Opelousas Waltz which is a completely different tune).