You might want to consider both right now. Last I looked the things I loved about couchdb (rest, replication, _changes, this couchapp design doc idea) do not have an equal in mongodb. 

I mentioned mongo in another thread simple because it's the "other one" and didn't realize update functions can take care of revision conflicts.



On Apr 6, 2011, at 4:10 AM, Benoit Chesneau <bchesneau@gmail.com> wrote:

> On Wed, Apr 6, 2011 at 10:03 AM, bryan rasmussen
> <rasmussen.bryan@gmail.com> wrote:
>> Hi,
>> 
>> I'm worried that in the future I might need to move to MongoDB, and if
>> it becomes necessary to make that move I should do so fairly quickly
>> (this is very much a 'be prepared for eventualities 6 months from now
>> sort of thing'), so I'm wondering if there are any tools out there to
>> make such a migration easier, and if there is anything I should
>> consider when making my couchdb databases in light of a need to
>> eventually migrate.
>> 
>> My main worry is having data that expands very rapidly
>> 
>> thanks,
>> Bryan Rasmussen
>> .
>> 
> I would only think about it when the problem come. Also you have
> different alternatives to mongo if you're worry about elasticity:
> 
> couchdb-lounge (? status)
> bigcouch/cloudant
> 
> and some other that could come.
> 
> - benoît