Previously I used 10mp5 on the basis that if it let me trade a haste/mp5 piece for a crit/haste piece keeping my regen OK, it would be the better enchant. But ive seen more and more top-end resto shamans using 10stats.
10 stats gives you roughly:
10/11 stamina (small surviving boost, but there)
12 int = 180 mana, 1.8 mp5 with replen and 43 extra mana per tide totem.
0.7% crit
2sp
Not sure if the stats are right but the healing benefits of 10 stats seem quite small, and the extra regen from 10mp5 seems greater but stacking Mana Tides closes the gap. So what is better? Assuming you're not blindly stacking mp5 and actually manage mana a bit to not go oom.