Both versions are equally efficient in helping you maximize your refund or minimize a liability but the greatest difference between the two is your commodity in using one or the other.
First thing to consider is a payment for the software. Online version allows you setting up your account, entering appropriate information, and getting a general feel for the product. You do not pay anything until you are ready to e-file your tax returns. This offers a benefit to the first time users; try it out, see how easy it is to progress with your return and whether you understand the questions, and if you like it and feel confident, purchase it. It is also a great opportunity for those who prepare taxes on their own for the first time. If you one of those people, you will be able to determine whether or not you can do it on your own, assess difficulty level, and overall feel for the process. CD/Download version must be paid for upon purchase. Pay first, use later. This of course may not matter to those who used it in the past and like the product.
I think that Online version holds an edge over CD/Download with respect to accessing your account. Online version can be used from any computer with Internet connection. If you’re on the go a lot this may provide a better solution. CD/Download version is confined to the computer where you installed the software. This brings up another point, and that is software updates. You don’t have to do anything in that department when using Online version. Any product updates are automatic. CD/Download does require you to keep up with the latest updates to ensure proper software functionality and being up to date with the latest tax laws.
When completing the return TurboTax Online walks you step-by-step through the tax preparation process, asking you questions covering all areas of your life that affect taxes. It then fills out all the required forms for you. CD/Download does that too and additionally allows you to access and complete related forms as they appear on paper. Once you file taxes you get a copy of all the forms (complete tax return) regardless of the software version you used. To view your completed tax return, access Online version from anywhere and see the returns. CD/Download version is stored on your computed or a drive (hard, flash, external) and it’s the only way to review the returns.
Finally, with TurboTax Online you can e-file one federal return and up to five state returns using the same user name and password. For every e-mail address, you can file five federal returns as long as you use a unique Taxpayer Identification Number (TIN) as well as user ID and password. CD/Download version allows you to e-file up to five federal tax returns and up to three state returns per each federal return. Using this version, you can prepare returns for as many states as you need but any additional return has to be printed and mailed. Both versions charge additionall fees for e-filing state returns.