I have an ipad for dd1 (she used my itouch for a couple of years before getting an ipad). I also have an android phone.
for overall ease, I woudl go with the ipad.
yes, you are paying for the brand name, to an extent. but you are getting more app availability with that (I know the android apps are ever expanding), and, imo, better ease of use.
finding apps via the appstore in itunes is, I think, a LOT easier than finding apps via the android market. so much so that I haven't even browsed for new apps for my phone in over 6 months.
I haven't loked at the assisted communication apps for android, but it is true there is a great range fort he ipad. proloquo gets good reviews, I can vouch for iprompts, there is the makaton one, and a whole host of others.
I have also found it easier to get recommendations for educational/useful ipad apps for children (and SN children) via websites, whereas the andorid ones I have looked at have not focussed on children's apps at all (or only games, rather than educaitonal)
finally, if there is ever a problem, the genius bar in apple stores is brilliant - very knowledgeable and helpful. you wouldn't necessarily get that kind of follow up with a tablet.