Personally I always go MD+LVM. It is faster (MD can do parallel reads in RAID1) and it requires only 2 disks (if you do not want to rebuild the mirror after every reboot) and MD is designed just to do RAID, and it does it very well. It is also more flexible.
Also I have been burned by LVM. In one case it was LVM striping on HP-UX, (should not happen w/ LVM2 in Linux), and I could not extend the LV because the extension had to have the exact same number of stripes. It seems reasonable, but sometimes …
Another time it was with mirroring (LVM2 in Linux this time), but now I cannot remember if LVM refused to take a snapshot of a mirrored LV or to extend it, effectively negating the benefit for having LVM in the first place (we did it in the end, but involved using lvconvert back and forth).