Very early on in my therapy - when I first became aware of my alts - I definitely used 'I'. 'They' were 'them' and were absolutely unwanted.
As therapy progressed and 'we' became more cooperative, we referred to us as 'we' when talking about the group as a whole, or only several members within the group - but only to Ts and a few close friends that knew about the DID. With them 'I' was used only when the front was talking solely about themselves. With others we tried to use 'I' all of the time, but sometimes slipped up.
Post therapy (and not fully integrated, but mostly) I use 'we' only very, very rarely (such as in this post!)
When in the thick of therapy 'we' seemed the most natural and accurate thing to use... because we were a we, and it simply would have been *wrong* to use the singular 'I'!
Now that I *own* all of me 'I' is the most appropriate to use. One alt wrote some of this with me, and while I acknowledge her as her own separate self internally, she is also now an 'I'.
(Don't know if that made any sense to anyone but me!)