The freebsd mailing lists are full of people using ataraid on Intel chipsets and losing all their data due to a single corrupt drive. Most of these are using ataraid for raid5, not realising that the ataraid code doesn't actually do raid5. Internally, it's just doing a raid0 stripset.
RAID1 should be okay. But ataraid works at a different level in the hardware stack than geom_mirror, and can't be combined as nicely with the rest of the geom_* modules. Useing geom_mirror is much nicer/easier than ataraid, as it's metadata is portable between systems. ataraid not so much.
Basically, ataraid should be avoided.
Using software RAID is fine (gmirror, graid3, graid5, zfs, etc). Pseudo-RAID is not.