SATA can theoretically write/read faster than parallel ata and is the newer technology so I would guess that most/all new drives will be sata
sata can theoretically do 1.5gb/s or 3.0gb/s, but can usually only sustain ~800mb/s (100MB/s... lets be optimistic ). ATA theoretically can do 133MB/s or 1064mb/s, but most can only sustain ~500mb/s. I would suggest checking out tomshardware harddrive charts for comparisons of speed and seek times and such for many drives
you're right, SATA vs ATA won't have a huge difference, kind of like AGP to PCIe x16, it's still no notable difference. Just one still operates good now, & one will operate the same/better & has future-support