A better question would probably be why a company went with one over the other. And how much use they are truly getting from these tools. I have worked for companies that have both Mercury and Segue at the same time and I will say marketing always plays a role but in the end (at least for me) it is how successful can we be with a product and how good is the customer service.
But in the end doesn't it all come down to BEER? Beer is the ultimate answer to all questions in the universe so yes the answer to your question is BEER.
In my experience the decision to buy a tool has little to do with the input from those who are going to actually use it. Time after time people go looking for tools and get suckered into the 'ease of use' trap and then set out to find inexperienced (read:entry level) people to use the tools. Then they are disappointed with the people that can't seem to make the easy-to-use tools to work without any training. I've worked with a good number of companies large and small who use Segue products and are getting their money's worth on the initial purchase. I also know a lot of people who have them on the shelves because they find out that using a tool is more than just clicking on a button that says "Test My App". Asking a company in a survey which tool they use, is really just asking 'which tool did you most recently buy?" Most aren't really using them to a large degree.
I think that the bottom line is that you can get good usage from either tool. Market share is the way it is because of marketing, not based on the quality of the tools. Do a survey of NASCAR mechanics which tools they use and I think that you'll find that they aren't the tools that have the largest marketshare.
Thanx for your inputs. I was basically focussing on a survey, to understand the software industry/ market on load testing front.
We use Silk Performer to a large extent for our clients and Loadrunner from Mercury Interactive seems to be in close contention with Silk Performer and I just thought this was due to Mercury Interactive's better marketing strategy as compared to Segue.
However, since I have worked on both the tools, I think Silk Performer has better features as compared to Loadrunner.
Since you've worked on both the tools, could you provide me the comparison between these tools and also let us know which are those features of Silk Performer that are better than LoadRunner's .