Hi Michelleh,
You will find differing opinions on this. Most of the Local SEOs I know use Localeze over UBL these days. I have seen doubts expressed regarding the current value of UBL. I have not used Yext, personally, but recommend you read Mike Blumenthal's recent review of their product:
http://blumenthals.com/blog/2012/03/01/yext-local-seo/
I'll quote from Mike's post here:
"Pluses:
-From a management and process point of view for the local SEO the service makes sense. Its fast and efficient and provides some tracking. What would take 6 or 7 hours is done in 15 minutes. If outsourced it would cost in the range of a $100 but the quality and consistency would not be as good.
-It seems to generate between 5 and 6 additional citations that Google thinks are important. Why that should be the case with listings that have already been claimed is not clear.
-The service allows for specials to be easily created and disseminated quickly and things like hours to be changed in a timely fashion.
-There is some reporting and there is decent multilevel management so an SEO can allow clients to access their own reports.
-If a business were to move or change phone numbers it provides a very efficient way of grappling with that issue.
-Whether you use the service or not, Yext’s Local Search Scorecard is a great way to assess NAP consistency across a wide range of sites.
Negatives:
-The reporting is lame. Although in conversations with Yext’s Howard Lerman, they will be adding additional features and color. One of particular interest will be review tracking.
-The cost in and off itself is expensive and it is an annual recurring cost. There is a small reseller discount that starts at only 5% and with enough volume goes up.
- Web traffic from these sites is small compared to Google and even comparing to Bing or Yahoo. But that isn’t Yext’s issue."
I think the main concern with Yext's product is its cost. If you can afford it, it might be a good choice, but as I've said, most of the Local SEOs I know appear to continue to favor Localeze.
And, there is the alternative, as pointed out well by ITRogers, of doing this manually and making your own spreadsheet to keep track of your work. I don't consider this inferior to any product being offered because you have total control over exactly what you are doing. In many cases, manual submission might be the best choice, and if you do it yourself, it is certainly the most affordable!