Here are my reasons for preferring Kanchi:
1) Ananya is an 18/19 year old young woman, with an innocent persona! Sai can NOT play an character who is that young!
2) The role of Anu is pretty much "tailor-made" for Kanchi...she suits the role perfectly...she portrays Anu's innocence and naivety extremely well
3) Yes, I know that sometimes Kanchi's acting is not that good and tends to be a bit "weak", but she is the original heroine of the serial. The serial is supposed to be ABOUT her. We have watched her for so long, going through her trials and tribulations, through the bad and the good, it is not fair to the viewers to change her.
4) No offense to anyone, but Sai is nowhere near as beautiful as Kanchi. Kanchi is a fair, tall, and beautiful girl. Sai needs to wear like 5 inch heels to even look as tall as Kanchi.
5) Sure, I agree that since Sai and Shakti are married, they will probably have good chemistry....but this is not always true...many real-life couples have POOR on screen chemistry (ex: Vivek and Aish (when they were going out), or Tom Cruise and Nicole Kidman (when they were married)). ALSO, Shakti and Kanchi have amazing chemistry...so why mess with it?
Well ladies and gents, that was my little rant....lol