No, they’re not equally well-coded. Some are better than others. Frankly, the ones that you have to pay for will be better than nearly all the ones that are free. If you want a great template, pick something like Genesis. I use it on my own site, and we use it on all of our client blogs as well.

As far as using interior page formats versus others, I don’t know the answer to that. You may have to modify them individually, IF you can get to the code that lets you do that. (Something tells me that will take some hotshot-level coding to be able to do that, but I don’t actually know.)

@joanmuschampfagnani Some have cleaner code that others. I always go for the premium ones because of the support and continued updates to match WordPress.  StudioPress, Thesis, and Elegant Themes have been the ones I use most between my own sites and clients.  I wrote about the differences between them here:
http://kikolani.com/thesis-vs-genesis-comparing-premium-wordpress-themes.html

Since writing that post, I have found that most people are leaning towards StudioPress because of their design options.  If price is an issue, then they go for Elegant Themes because it’s so inexpensive (one year for $39 gets you access to over 70 designs).

Hope this helps!

Joan, the last time I looked at Elegant Themes, mainly because it was so cheap, I was eager to use them because of the cost. But when I start digging in, looking closely, I realized most were a bit too artsy and the type a little too difficult to read. Beautiful and elegant, but not as practical as I had wished. Taking classes on Adult Learning was part of my Communications major in college, and one thing I’m glad I learned young as an editor was never to choose typefaces that ALL ages could not read because it limits your audience. Now that I’m an old gal, lol, I’m kinda wishing more people would go less for the pretty and more for readability, especially online.

I just Looooooove Elegant themes… so very pretty… but can’t read most of them… So for me, it’s either stick to free themes or pay a lot.

Just my thoughts…

Robin

Joan,When using ANY theme from ANY place or ANYone free or otherwise, it is always a good idea to make sure that the theme is clean and free from any malicious codes or links as @loumacdonald mentioned in the previous post.  Word Press makes a coupe tools that I and other marketers have found very helpful for detecting these and other things like the themes authenticity in the themes used.These tools can be located here:
Authenticity Checker - http://wordpress.org/extend/plugins/tac
Vulnerability Checker - http://wordpress.org/extend/plugins/timthumb-vulnerability-scanner/
Hope this helps and Happy Blogging