Framework does matter
I assume you don't have any expertise on any of this anyway so why choose one randomly? If you are expert or really good in of the options go for it, don't think twice. If you are not my comments:
If it's a classical bunch of CRUD + AJAX stuff and if you can find RoR developers go for it, because it'll be much faster others (assuming developers are experienced in in RoR).
Don't go for PHP, it's dying not that agile unless you got some really really good developers. Lots of things is painful, It's not suitable for unit test, new versions breaking old stuff , there are performance issues, not suitable for big projects etc. Just stay away.
Don't go for J2EE, that's designed for Enterprise rubbish, even for the smallest task you have to spend ages to develop, deploy and test. Also J2EE developers are mostly in this mindset as well, so stay clear.
.NET is not too bad but license cost is high, development is not as agile as RoR, components are expensive, however if you are going to build a big system and need performance then .NET (ASP.NET MVC not the old way) is your guy. It's easy to find good developers as well, they are all over the place.