What's the difference between the two?
Isn't a custom Wordpress theme, by definition, a custom website?
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When it comes to design, there are really three things great web design needs to do:
Maintain your branding
Whether it's showing off your company "personality" (professional, high end, friendly, old school) or just keeping the color scheme and logo from your trucks, business cards, and letter heads, your website shouldn't be some crazy step out of line. When you're iPod breaks and you go to the Apple website to replace it, you would expect it to be a clean, sleek, and easy to use, not some Victorian antique looking looking thing.
Define hierarchy and goals
Good design makes things pretty. Great design makes things important.
A lot of people (and most of them rightly so) think designers are just making your site look sexy. When I was starting out in the biz I found that to be incredibly true, and thankfully I started working for a shop that who's owner prized form with function.
Great design draws the eye to important elements (call to action, contact form, phone number, portfolio, whatever), while dimming down less important aspects on the page.
Your pages won't be nearly as effective if you have a ton of options, or a ton of pictures, or a ton of headings, or a ton of crap. That's just another bonus of keeping things simple.
Define an important business goal, make a page, and then define what's most important on the page while finding a way to make it prominent without it being lime green
Most importantly, be easy to use and geared towards your visitors
The sexiest web design in the world won't do jack balls all for your Christmas spending or vacation fund if it does any of these things:
Confuses the visitor about what the site's about (Is this a mason, plumber, carpenter, day care, car wash, coffee shop, 7th circle of hell?)
Makes it difficult for the visitor to find what they need
MAKES EVERYTHING HUGE AND IN CAPS SO I ACTUALLY HAVE NO IDEA WHAT IS IMPORTANT
Sticks important info/coupons/goal conversion stuff all the way at the bottom of the page, or real small in the corner somewhere.
Has no clear steps for what to do next if I want to buy right now/set up and appointment/call you for more info/shoot you an email for clarification
You shouldn't pay a web pro to make your site look pretty. You should be paying for them to give you a tool to make money. Luckily, the two don't have to be mutually exclusive.
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I personally absolutely hate Artisteer with every bone in my body, but then again I hate any piece of software that boxes you in and at the same time pumps out crap code. To me, the web is about freedom and flexiblity. You can polish and shine that turd, but at the end of the day it's still stinking.
I'd rather spend the extra day or two it takes to code it myself and give the client something lightweight that I know is solid, than trust their business to a piece of junk like Artisteer. There are a lot of tools out there that will help you speed the process up without having to trust your bank account to a robot.