head on down to the IJN section i searched CV and got this:

http://navyfield.com/Community/Forum/View.aspx?num=6212&searchtype=0&pagecount=0&searchvalue=cv&sort=5&category=A03&page1=1

more time and a few different words will give you all you need to know.

i will say i have played down both IJN CV lines and in general i HATED the tahiao but loved the rest of the junyo line, but the tahiao is the one you in for longest.

the hosho you change ships quicker so gives more of a incentive.

Hosho isn't bad for your 1st CV line as you get more options faster as camb has said.  I found the Junyo line CVs to be more manuverable on average and more fun but that's just me.  I enjoyed the Taiho so its more  a preference thing but the Shokaku (Junyo line after Taiho) is much better than the remodeled Kaga (equivilant CV on Hosho line) and you get it 2 levels faster.