2 domains, which to 301 redirect to the other?

[lchrzan]

This is somewhat complicated but I think it is worth a discussion.
I have a client that has 2 domain names.
Let's call them www.companyname.com and www.oldcompname.com.
Neither is 301 redirected to the other, and I want to do that.
Obviously I'm worried about duplicate content.

The preferred name is www.companyname.com, as this is...surprisingly enough, the company name.
The www.oldcompname.com is an old name of the company.

Here is the pertinent information:
SERPs
www.oldcompname.com has a lot of top 10 rankings on Google for many good keywords that are driving traffic to the site now.
www.companyname.com has only one keyword that is ranked on Google.
On Yahoo, it's a mix - www.oldcompname.com and www.companyname.com are both ranked for some words and each is ranked sometimes without the other.

Inbound links according to Yahoo
www.oldcompname.com has 26
www.companyname.com has 50

Indexing
Running the search site:www.oldcompname.com on Google shows 43 pages indexed.
Running the search site:www.companyname.com on Google shows 197 pages indexed.
Running the search site:www.oldcompname.com on Yahoo shows 58 pages indexed.
Running the search site:www.companyname.com on Yahoo shows 118 pages indexed.
The SEs find the catalog pages for www.companyname.com, not for www.oldcompname.com.

So what I would like to do is do the 301 redirect from www.oldcompname.com to www.companyname.com.
www.companyname.com has more inbound links and is better indexed.
But I am worried about losing all those rankings on www.oldcompname.com, especially on Google.
This could have a big impact on business.

What would you do?

[incrediblehelp]

This is a business decision more than anything. If you need to change the domain name, you need to change the domain name. If you don't then don't.

So if you have to, just bite the bullet, implement the 301 redirects and in time the rankings "should" come back. While the search einnes catch up, build up good links to the new domain.

[incrediblehelp]

Moved to Search Engine Optimization Forum