I think the default style template is Blue Temptation. Most people love it and its fast on any device.
I am installing several new style templates over the next few days. And I have been messing with the Flatmaster Blue Edition style template the last few days. This is a little bit thicker heavier template and may react slow on some computers.
Remember you can change themes at the bottom right of any page. And you can always change back to the Woltlab Basic or Blue Temptation style if you don't like what you see.
Here is a screenshot of the Flatmaster Blue Edition template running.
P.S. I have a new template I'm finishing up on that is a surprise. I think it may be the best looking website template ever. I will try to have it available tomorrow.