If you want to run a successful MyBB forum, you’ll need something else then the default theme.
You’ll need a MyBB design that makes your site unique. If your site looks like all of the other MyBB installations with the default theme, you’ll get less attention and make less money if you use MyBB for Business.
The best choice to provide your visitors with a unique experience is a custom unique theme by a webdesigner. It should match your main topics, for example by using background-images or graphics that remind visitors of the topic. If you are hosting a gaming related forum for example, you should have a more futuristic MyBB theme. If you are talking about money, you should use a serious looking theme that is not as playful as gaming related themes.
If you can not afford a custom theme yet, you can go for a premium theme. Good non exclusive premium themes are available for 20$ or more. They usually contain no backlinks to the authors site and will not downgrade your pagerank.
Make sure that the theme is well coded. Check the W3C Validator to see if the theme is coded with valid HTML and valid CSS. Also check the Google Pagespeed Tool to see if the theme does not load unneccessary javascripts and performs well in terms of speed.
Make sure that the theme is kept up-to-date and actively supported. Good MyBB theme developers are also well-known in the MyBB community and have a good reputation.
If you are testing a new MyBB forum and don’t want to spend money on a theme yet, go for a free MyBB theme. There are approximatly 100 free MyBB themes available for MyBB 1.8 at the moment.
They usually include a backlink to the authors site that may not be removed. This can downgrade your pagerank. Remember that free MyBB themes are often not tested intensively and may have a bad quality.
If you don’t want to rely on a theme by a foreign developer, you can use the MyBB default theme. MyBB 1.8 ships with a theme that contains multiple colors, better choose something else then the default blue. It’ll at least make your forum a little bit more unique then the other MyBB forums.
Mobile ready themes
The best theme choice today is a theme that works well on desktop computers and mobile devices like smartphones or tablets. Since MyBB does still rely on tables for the layout, it is quite difficult to get it working properly on small screens. There are only a few responsive MyBB designs available for MyBB 1.8. If you can get a responsive MyBB theme you should definately take it if it fits your forum topic.
So how do you find the best theme for your MyBB?
For starters you should check out some different MyBB themes. Mybb Design has a nice preview function for themes so you can check out different styles easily. Be inspired!