在一个新项目中使用mongodb, 选择Object mapper的时候，看到官方的推荐，我凌乱了：
Several mappers are available:
MongoMapper from John Nunemaker
Mongoid from Durran Jordan
Mongomatic from Ben Myles
MongoODM from Carlos Paramio
MongoModel from Sam Pohlenz
DriverAPILayer from Alexey Petrushin
搜索了一下，“哪个OM最好？”这样的问题在stackoverflow上被关闭了，不过这个文章非常有帮助：
http://stackoverflow.com/questions/1958365/mongoid-or-mongomapper
问：mongoid 还是用mongomapper
17票， Aynat答：
I have used MongoMapper for awhile but decided to migrate to MongoId. The reason is hidden issues plus arrogance towards users. I had to jump through hoops to make MongoMapper work with Cucumber (succeeded in the end) and to put a couple of patches even the project was simple, but it's not the point. When I tried to submit a bug fix (due to incompatibility with ActiveRecord), they seemingly got pissed off that I found a problem and I was pushed around. While I was testing, I also encountered a major bug with their query implementation, while their testing was tuned in a way that the tests pass. After my previous experience, didn't dare to submit it.
我用MongoMapper已经有一段日子了，不过最近决定要换成MongId。 mongomapper的人太自大，她们有BUG（比如不能跟cucumber兼容）也不愿意改，我提了PATCH他们反而觉得很愤怒，估计他们自我感觉太好，自认为产品美文体。而且mongomapper的查询接口太差劲。我还得做一些修改才能让代码工作。我不介意修改代码，但是由于之前的不好的经验，这次我不敢提PATCH了。。。 而且， mongoid的社区（提交代码的人啊啥的）比mongomapper的强太多了。
5票， mtkd答：
Did some testing with MongoMapper last week, it was stable but I found the query interface a little limited (also some of the AR logic was quirky), switched to Mongoid today and it feels much better to use - and more intuitive if you are used to AR.
上周对MongoMapper做了些测试，它确实稳定，但是查询接口还是不太理想（而且有的active record的逻辑也很奇怪）， 今天我换到了mongid上，用起来舒服多了。而且对于熟悉AR的朋友也很直观。
30票，Nader答：
(2010年一月答案）i've been using both for the past couple weeks. Mongomapper has better support for relational associations (non-embedded) and has greater third-party support. Mongoid has better query support, much better documentation (MM has close to none, though a website is supposedly in the works), Rail 3 support (and thus Devise support) and a slightly more active community on Google Groups.
I ended up going with Mongoid.
这两个我都用了几周。Mongomapper对于关联支持的很好，而且被很多第三方工具支持。 Mongoid的查询接口做的更好，而且文档也强多了（MongoMapper的文档都关掉了(?)）。Mongoid还支持RAILS3，它的论坛也更活跃。
(2011年一月追加答案）
Since I originally wrote this answer Mongoid has picked up lots of third-party support and the difference in the communities is even greater. In my opinion Mongoid is more of a clear choice today. Performance should be relatively the same as they both go through the Ruby driver. Though you need to be careful with OM not to construct horrendous documents. – Nader Feb 1 '11 at 0:53
过去一年里，MongoID 被更多的第三方工具支持，所以它们的差距是越来越大了。在我看来，现在Mongid更好了。我们应该毫不犹豫的选择它。 它们在性能上估计差距不大，因为用的都是RUBY的驱动。
其他几个答案也很吸引我，可惜被关掉了：
Which Rails Object Mapper to choose for MongoDB? [closed]
从这个文章（
http://praktikanten.brueckenschlaeger.org/2010/11/23/do-i-use-mongoid-mongomapper-or-mongomatic-as-my-ruby-orm-for-mongodb） 中 有 三者的对比（mongoid, mongomapper, mongomatic). 其中对于mongomatic的说法是：简单：
mongoid:
better support for embedded documents
better support for very large documents (>500kb)
closer to activerecord, by making use of active model and an arel like query syntax
very nice and lean documentation to be found on the project website..
( 对embedded documents支持的更好
对大数据量的documents支持的更好（ 》 500 KB）
更activerecord非常类似。使用了arel查询。
简明扼要的教程，非常棒。)
mongomapper:
better support for reference associations
supposedly it has a bigger community, or at least still had a bigger community last summer
better plugin interface
(对关联支持的更好， 社区很大（起码在写文章的时候，2010年夏天）， 对PLUGIN支持的更好）
mongomatic
supposedly it’s faster. there is a benchmark posted on some blog. The benchmark itself can be downloaded on Github
it says it focusses on simplicity
（据说是最快的，官方文档说，它注重的是使用简单）
更多的文章都是2010年的了。。。呃。。。有点儿老旧，我还是用mongoid的（忙高一的）