Disclaimer: We run 10 Million Unique visitors a month through Groovy/Grails on Virtualtourist.com and I have been a Linux Java guy since 1998. I have also run/lead Asp.net, Perl, Cold Fusion, PHP and Ruby/Rails sites/teams so I am generally versed in the big frameworks.
If we agree that there are really only 4 valid mainstream options:
Then we either need to talk about your target market, your budget, or local access to skills.
If you have no budget for licensing, then the closed M$ system is out.
If you have no budget for development and you are B2C then PHP "Visual Basic for the Web" is your best chance. But you are not going to scale to enterprise level, and good luck finding high quality developer talent. Like VB, PHP developers are easy to find and inexpensive by comparrison, GOOD PHP developers are mostly white whales who would rather be working in another language (Groovy/Ruby).
If you do have some budget for development, and scale or B2B are part of your SAAS, then you really have a choice between Ruby/Rails or Groovy/Grails. Both can run on AWS, rightscale, or various other providers e.g. Heroku etc.. Both can talk to various NoSQL or SQL solutions, likely to need both. Both Scale to reasonably degrees. Both have libraries for Enterprise type integration, both make reasonable SAAS platforms. Both have plug-in ecosystems for development. Java is obviously more mature with more libraries depending on your requirements. Both can talk to SOLR or Elastic Search. All of them are going to be run behind Apache (except M$ stuff of course).
Now you are really in a conversation called what local talent is available, and how do I attract them?
I find that I can find lots of talented Java developers who are excited to work on Groovy/Grails/JVM here in the L.A. area. Ruby/Rails guys here tend to be a little more expensive and harder to find.
Fundamentally, I don't think you should be thinking at all about what data store No SQL/SQL you are using Mongo/Postrgres/Cassandra/Redshift/Memcache/ et al... You aren't qualified to make that decision, nor am I with the little information you have given us.
At the end of the day, if you are approaching Enterprise class customers, you are going to want to go with Groovy/Grails because of Spring/J2EE and JVM being under the hood. Enterprise class customers are going to see the SPRING platform, ability to buy support etc... as a comfort.
If you are looking for funding, that may also change your choice. Some VC's have tech people they are comfortable with in either PHP/Ruby/(Java/Groovy)/.NET and they may be more or less likely to invest if they are familiar/experienced with that particular platform. Your strategy on this front, might actually dictate/limit your choices.
Food for thought.