When I started my first blog I picked up a very basic WordPress theme that has all the functionalities I needed and changed few bits and pieces here and there. If you want simplicity then you can simply pick up a basic pre-made theme and modify it which is quick and easy. The benefits of tweaking or using pre-made WordPress themes are you save a lot of time to get your website up with a nice theme design and you do not need to know a lot about CSS, XHTML or PHP.
If you are after a Unique and Stylish theme to match your needs then the theme needs to be created from the scratch so that everything displayed caters to the specific kind of content that your site offers. You can be creative with your design skills if you design your own theme and your site will be unique from other sites.
At the end of the day I figured out that I have tweaked my theme so much that it doesn’t look anything like the way it was. So it is better to create your own WordPress theme once you understand the basics of the theme and it is lot easier to tweak using that knowledge. Adding a banner to the header or changing you contact details in the footer can be simple and some themes already give you the option to change it but with out knowing how exactly WordPress theme works tweaking could be time consuming because you wont know exactly what to change and what effect it will take. I agree you do not need to know a lot about CSS, XHTM or PHP to tweak or create a new theme but you definitely need to have a clear idea how they work in the theme.
WordPress Codex site has got very good documentation for how to create a WordPress theme but for the beginners it could be a bit complicated. I found out other websites straight jump into coding and get you a basic theme structure without explaining much. Mission might be accomplished but you would be still starching your head and thinking what to do with that theme.
In my WordPress theme design tutorials, I will try to keep it very simple. I will explain the structure of the theme, how to use PHP to call WordPress functionalities and CSS to create stylesheet. Once you learn the basics you can be as creative as you like.
WordPress Theme Design Tutorial 1: WordPress Theme development tools
Tagsthemes for wordpress, WordPress