Need Help: What is good alternative for MongoDB?

There is long discussion on mongodb issues/failures at http://pastebin.com/raw.php?i=FD3xe6Jt in post http://news.ycombinator.com/item?id=3202081.

I have bet my next product on mongodb. Now I am worried see issued mentioned by others. what are my options now ...

My DB Requirements

Need a database which can handle large load and should be able to scale as the application usage grows. It is some use cases similar to mixpanel. Need nice query capability also which mongo db was good provided.

What do you guys think is an alternative to MongoDB ?

(a) Riak

(b) HBase

(c) Cassandra

Or I should just give-up noSQL and go back to RDBMS.