My previous weblog was hosted on Rediff blogs at http://ashishg.rediffblogs.com. I just had this account to write in for Sangam weblogs. Anyway, here let me recount some of the advantages and disadvantages of Rediff Blogs and Blogger.
Blogger.com is obviously designed for blogs specifically, and hence it has most of the interesting features, and many of them are useful for an average blogger like me. However what I like particularily on blogger.com is the WYSWYG posting so that you can compose and edit your posts in all coloursful formats without knowing html language. Also one can get email notification when a visitor leaves a comment on the posting which is lacking on rediffblogs.com, and which is very important feature. Another useful features, though not particularly of interest to me, are ability to post on server other than blogger.com, detailed profile of blogger, more templates to chose from etc.
However though I dislike the absence of the comment-notification feature in rediffblogs.com, I like the ability to categorize your posts into various groups, which is unavailable in blogger.com. Apart from this rediff doesn't have any advantage, and hence, I shifted from rediffblogs to blogger.com.
All these differences are, of course, assuming that, you don't want to do major overhauling of script.