I manually shift mine, just because there is something wrong with my tranny.. however when my mom used to drive her, she was always in OD. Your preference.
1st = only 1st gear
2nd = 1st or 2nd gear [automatic]
D [3rd] = 1st, 2nd, 3rd [also, automatic]
OD = 1st, 2nd, 3rd, 4th [once again, automatic]
With your newer cars, often times it will automatically bypass the gear selector, and shift if you go to redline. This happend with electronic shifting, where the PCM controls the transmission'* shifting, unlike manual shifting, which was mechanical motion shifting the transmission. I think this came originally with the Hybrid ECMs [I don't know when for our cars], however I think it really only came into all cars in full OBDII 97/98 range. Anyways, pretty off topic there, sorry 'bout that