I use both AIO's but majority of my stash is pockets - although AIO's are easy to use and depending on what kind you are using (ie. itti bitti d'lish) they dry relatively quickly and are very popular.
Personally I would suggest getting pockets with more inserts for the simple fact that you can adjust absorbency according to what time of day it is - ie. nights she has cotton flat & hemp/bamboo trifold, during the day, say afternoon, she has just a microfibre insert which works fine for 3 hours. The pockets themselves dry in a flash as well.
It is a little more work with having to stuff the nappies then using AIO's, nothing major though