Which framework should I use (RoR, Grails, Java/Hib/Spring)?

I would use whichever framework you believe will allow you to deliver features most efficiently while building your project. Any of those frameworks can scale to support a large volume of users and leave you with well known paths to scaling further if you are so fortunate as to need to. Having used both Spring and Rails I think I would favor Rails for any new project. I find development in Ruby much faster than in Java and think it would be a net win even when accounting for the learning curve of developers new to the language and framework. I have found that the Ruby community provides a great set of tools to solve many common problems and the html templating options and javascript integration in Rails makes building the front end of a site much easier than anything I found available with Spring. Whatever you choose some reasonable db indexes, web server caching, and a well designed set of stateless controllers should allow you to easily scale to the limits of a large single database instance. That's way more than enough capacity to learn that supporting even more users is not a problem. Instead worry about building a product which can actually start to attract that volume of traffic. Even rudimentary monitoring should give you an idea if you'll ever need to worry about sharding your database or making other architectural changes to support increasing traffic. Unless you happen to have a large pile of money and a bunch of time you want to burn don't scale prematurely. Make reasonable decisions guided by any of these frameworks, monitor your growth and performance so you know when you need to make changes and more importantly what you need to change, and focus on building valuable features.

Give the java/scala based Play! Framework a try - http://www.playframework.org/Watch the 8.5 minute tutorial ... it seems to be a powerful webapps framework that borrows principles from the RoR world. In addition to (http://www.playframework.org/), there are many -based web and web service frameworks, and the stack is mature, modern, powerful (for example it is used for the demanding parts of 's back-end) and supported by companies like : http://typesafe.com/

Not only would I say you should go grails, I would say we went grails and are loving it.  Java developers are up to speed in weeks and wildly more productive within months than they ever were in java frameworks.  Love the JVM ecosystem over RoR and Ruby still occurs to me like the next generation of Perl. I don't find it readable imho.   We are handling 8 million unique visitors around 25 million page views through grails at http://www.virtualtourist.com One more tought that some people seem to miss.  Grails uses Spring and Hibernate under the hood, so if you have those skills, the transition to Grails is very quick.

In my opinion, you should go for Groovy on Grails. You can write code in both Java and Groovy whatever you like. It will give you both scalability/performance, there is GORM on top up hibernate ready for you. You can easily integrate with any frontend frameworks jQuery, angularjs or emberjs.

First, if you will have problems with the scalability then you will be lucky. That means your application has traction, lots of it. At this stage, I bet you will have investors and money to hire scalability specialists, rewrite your application and buy more hardware (or pay for the cloud). So, wait until you get there. Yelp took years to reach that level and I bet they have re-written their application several times to accommodate the growth (they use Python, Ubuntu, MySQL). Second, I didn't know about Groovy Rails (and Groovy language) and I bet many of web developers don't know either. That means it's pretty new and that means probably you won't find many web developers to know it or know much about it (including scalability). I see they have some cases studies but none are very high traffic websites, I think. But I heard a lot about Ruby on Rails and Java. Twitter was originally built on Ruby on Rails and just recently switched to Java and . That means RoR can be scalable. But again, do you think you will have Twitter's traffic? Or close to it? There are more examples of website built in RoR and some of them have high traffic: You can find RoR developers more easily  than Grails and even more easily you can find Java developers. In the end, you will choose whatever language you know best and if that is Scala or Java then why not? Like I said, you shouldn't be concerned with the scalability issue in this phase. It's too early and it's pointless. Instead just build the stuff. Whatever language you will use, when you will have scalability issue I bet you will have to rewrite the application and bring other improvements to it to accommodate this. Read this please: The Number 1 Reason Startups Fail http://techcrunch.com/2011/08/29/what-kills-startups-blackbox-releases-reportapp-to-help-founders-avoid-the-deadpool/ (premature scaling on all levels) [1]

Build small apps in each of them and see what you prefer. If your app is time sensitive just go with what you know as you'll get to market quicker. If you want to try Grails and get introduced to our community come on out for the Grails48 hackathon http://www.grails48.com and work on a project with one of the teams. Can't think of a better way to test out a framework than working with it for 48hrs straight with some of best developers within the community.

I'd go with Grails. You have the same agile high productivity web development of RoR, and the power of Spring/Java on the backend. If you're building a large scale web application, Java will scale and easily handle the complexities of a distributed application.

With the given choices, and my Java experience, I'd stick to Java. was already mentioned. Another choice would be JAX-RS REST stacks such as on the back end, and pure JavaScript + HTML5 on the front end. (This answer is late, so I presume the asker has already chosen one of the solutions.)

Stick with java and take a look at Google http://code.google.com/p/google-guice/  I'm using it with jQuery and it works great.  Much higher power to weight ratio than the heavy frameworks.  Watch this video on "Twitter: From Ruby on Rails to the JVM"