Hi Agarwal,
Thanks for the email, and glad you're having success with Spark on so many projects. I do actively maintain Spark and I fix any bugs that come in, but there is not much changing in the world of Spark. Personally I don't use MVC anymore since moving everything over to frameworks like Fubu, ServiceStack and Nancy depending on the client and requirements so I can't say I've ever done anything on MVC5 - the last version I worked on is MVC4. There should be no problem with Spark working with MVC5 however, and the latest Nuget has got binaries all the way from .Net 2 up to .Net 4.5 packaged inside. If someone wants to test it out on MVC5 and let me know if there are any bugs, I'll be happy to release a Nuget for it after fixing any bugs.
As far as the future of Spark is concerned, we've had absolutely zero help from Microsoft in terms of exposure of the project, and in reality, just like with some many other OSS initiatives, they've inadvertently ended up crushing the life out of innovation. I still consider Spark to be an excellent server side templating engine free from the contraints of System.Web which is something that Razor can never claim, and we use it in a ton of places like email templating, and CMS systems in SharePoint and many more applications, but it will never really be able to compete with something like razor unless a brighter light is shone on it. Personally I think that the world of the web is changing fast and that with client side templating engines written in Javascript like Jade and Handlebars, Mustache etc etc taking over the world, I would think even the days of Razor are numbered, but at least Spark has other applications server side that have nothing to do with the web, and while that is still the case, I'll still be maintaining it for as long as I can.
FWIW, the best source (because it's the easiest to deploy to) will always be Nuget unless that dies.
Cheers,
Rob