Dear Saran, we have missed your post and sorry for the late reply.
Both of these web hosts support unlimited number of websites on them.
No matter how many websites you develop per year, but the main factor is how many impressions all your websites at a particular account of a web server is getting per day.
If you have are getting small number of impressions per day, say less than around 2000, I recommend you to choose bluehost as your webhost. Because bluehost is reliable and faster than hostgator, but bluehost has a throttling feature which will slow down your website if you are getting huge number of impressions than that i said.
If you are getting large number of impressions per day, say above 3000, I recommend you to choose hostgator as your webhost. Because hostgator is more powerful and cheaper than bluehost. It support much more impressions than bluehost. Also hostgator allow some kind of p0rn~stuffs and are not so strict like bluehost.
So choosing your web host from bluehost and hostgator web hosting companies really depends upon you. Both of these companies have same features. I have used both of them