Neither of these are appropriate defaults.
First of all, web standards dictate that links should open in the same window. This is demonstrated in baseline anchor tag functionality, which requires explicit additions ("target") to be overridden. That is the first indication that new windows should be very carefully considered.
A second issue is around new window/new tab failures. Pop-up blocking has become a standard, opt-out feature of modern web browsers, and even an alpha geek like me has been left scratching my head after a click on a major publisher's website appeared to be dead, until I finally looked up at the alert area beside the address bar alerting me to the pop-up blocking.
Furthermore, depending on your user base, new tabs/windows could have catastrophic results on user navigation. The lowest-common-denominator of web users, IMO (I don't have data to support this so take it with a grain of salt), exhibit a linear browsing model. By this I mean that users click on things to move forward and click the Back button to retrace their steps. Introducing a new window breaks this linear flow and can lead to the user wondering how to get back from where they came (your site).
Power users who are more likely to embrace a New Window nav pattern probably have their own browsing patterns which include some manual form of opening links in a new window or tab (for me it's a CTRL Click on Mac).
By respecting web standards you can satisfy all use cases. Non-savvy users get the nav pattern they're used to, savvier users can still customize their browsing pattern, and the pop-up failures (and necessary workarounds and fallbacks) are eliminated.
If you think that new windows are a crucial part of your interactions then I would suggest adding an explicit "New Window" link (or whatever semantics you want to use) which will provide the same one-click new-window behavior you're looking to achieve without making the sacrifices I've mentioned.