Which database out of CouchDB, MongoDB and Redis is good for starting out with Node.js?

Is any one of them better suited for Node JS?

Better suited especially for node.js probably no, but each of them is better suited for certain scenarios based on your application needs or use cases.

Redis is an advanced key-value store and probably the fastest one among the three NoSQL solutions. Besides basic key data manipulation it supports rich data structures such as lists, sets, hashes or pub/sub functionality which can be really handy, namely in statistics or other real-time madness. It however lacks some sort of querying language.

CouchDB is document oriented store which is very durable, offers MVCC, REST interface, great replication system and map-reduce querying. It can be used for wide area of scenarios and substitute your RDBMS, however if you are used to ad hoc SQL queries then you may have certain problems with it's map-reduce views.

MongoDB is also document oriented store like CouchDB and it supports ad hoc querying besides map-reduce which is probably one of the crucial features why people searching for DRBMS substitution choose MongoDB over the other NoSQL solutions.

Is any one of them better for beginners, moving from relational databases?

Since you are coming from the RDBMS world and you are probably used to SQL then, I think, you should go with the Mongodb because, unlike Redis or CouchDB, it supports ad hoc queries and the querying mechanism is similar to SQL. However there may be areas, depending on your application scenarios, where Redis or CouchDB may be better suited to do the job.