I have also used both. I think Scrapebox is a wonderful application and recommend it to everyone. They have built so many cool features in their application I use it almost every day. However I do think in comparison to Paigham Bot and specifically contact form marketing Paigham Bot is a stand alone product for this specific marketing.
I have actually ran split tests in the posting module for Scrape Box and compared that to Paigham Bot. I composed the test by uploading a list of 300K + websites to both Paigham Bot and Scrape Box. I did not use any captcha solving nor any advanced form fields (in paigham bot so it posted the same as scrapebox) in our tests. After both application's contact form modules were done, posting Scrapebox had a 48.8% failure rate. Paigham Bot had a failure rate of only 30% (Which would have been lower using captcha solving and customized posting fields). See campaign results here: http://screencast.com/t/Q8y7g04qQ
Paigham Bot also, IMO, has a simpler user interface for a lot of users, and customization and ability of posting to more complex contact forms is much simpler in Paigham Bot from our users and our staff experiences. We have our tag control module which allows for easy drag and drop of form tags to allow a user to custom create their own form posting sequence.
During my test we also found that thread for thread Paigham Bot was faster at Posting to contact forms than Scrapebox (although currently Scrapebox has ability to run more threads than Paigham Bot but we wiill have an update coming which will increase multi-threading past 20 threads so this will level this out in terms of multi-threading and speed per posting. Paigham Bot Currently has potential to process 200 sites per minute).
I also found during our tests that Paigham Bot was able to find more contact forms per unique keyword entered than Scrape box (this is because of unique footprint spinning we have custom programmed into the application). You can see a video comparison on the scraping here: http://screencast.com/t/R0AxwWpLYPU (You can fast forward to end of video to see the results).
One of the unique features in Paigham Bot is also our smart niche filter. You can watch a video on that here:
These are just some of thee many reasons we believe that Paigham Bot is a stand alone product when it comes to contact form marketing. At least this is all my opinion.