Just wanted to know whats the big difference and which is better
They are 2 completely different apps, aimed at different aspects of modelling workflow and output.
T-Splines is ‘Sub-D’ modelling, and uses surface patches to create organic geometry.
It’s relatively easy to create complex organic shapes, and to have loose control over how they will look.
Very accurate modelling is difficult to do, if precise control over geometry is required.
Great for 3D printing etc, not so good for tooling grade data.
VSR is aimed at higher quality surfacing, in that it allows for precise control over single span surfaces and edge conditions.
Difficult to use skillfully, as the tools are aimed at producing simple, accurate surfaces - Class-A.
The analysis tools help to check continuity, especially important when developing parts for tooling.
I have both products, and use them for completely different tasks.
What kind of modelling are you interested in doing?
Hope that’s of some help.
The only thing I’d like to add to this is that since both plug-ins have been acquired by Autodesk lately, there is a big question mark over future development of the software.
In both cases Autodesk promised to be committed to the Rhino user base (while at the same time integrating the technology into other products: t-plines -> Fusion360, VSR -> probably Alias), but the t-splines plug-in hasn’t seen any updates for years and it’s highly doubtful if Shape Modeling will get its scheduled yearly update at the end of 2014.
Still both are excellent pieces of software IMO (I own and use both of them), you just should be aware that future development of both products is all but secured.