I am looking for a 3d modelling software which is easy to learn, convenient to use and delivers models to unity for my projects, yes i have used 3ds max 9 earlier, and it was good to use, but i am looking for any other software, and 3ds max is a costly one.
i am confused between Sketchup, Blender, and Chetaah3d actually…
I love Maya, it’s mostly straightforward to learn, yet complex and powerful. I found Maya more approachable than 3ds max, but it’s a good program as well, perhaps better in ways. I also like blender. It’s free, open source, and lots of tutorials of all sorts. It’s really comes down to a decision based on personal preference, but try some trials out, screw with blender, and see what fits you best.
If you are on a limited budget then I can think of nothing better than Blender. It is free and it is powerful, the last time I looked at sketchup I would have struggled to recommend it 
Blenders interface can be a little off putting at the start but Blender Wiki will help a lot, do the Gingerbread Man Tutorial in the Introduction Section. It will not only teach you the Blender 3D modelling basics but also Animation and the Interface.
After that there is a wealth of info and tutorials across the web and especially on you tube for traditional modelling and sculpting etc.