Robot WAS a very good application. It has been ignored by Rational and now IBM for many years. Bugs go unfixed and there are few if any enhancements.
Much of what made Robot successful was the community that used it and shared their experiences, knowledge and code. Because the application no longer growing most everything that needs to be said has been and the community is disintegrating.
Robot has been slated for End Of Life (EOL) with RobotJ (Or whatever it's called now) is supposed to replace it.
QTP is easy enough to use. Personally, I don't like the GUI map but some like that a lot.
I'm pretty sure Winrunner is slated for EOL too.
OK. Unfortunately I don't have the Robot software to experiment but the documentation here and there says that it can integrate with code coverage and quantify tools, it has comparators that support different formats, it can generate test data (any number of records) and so on... some of which are not available in QTP. So, I wanted to see what people say here. Hope IBM gives a trail software for Robot.
Robot is probably not going away, it supports the legacy apps (C/C++, Delphi, PowerBuilder). The potential replace is Rational Functional Tester (RFT), but it supports Java/J2EE and .Net based apps only.
Robot was loosing market share to WinRunner long before it was acquired by Rational (and eventually IBM). The key thing that hurt it was the object mapping capability. Because the object recognition method is captured in line with the command/function call it made maintenance of scripts a pain, especially in situations where code reuse was minimal. It could not support the Record/Playback paradigm everyone wanted. Mercury capitalized on that via the GUI Map (but even then it had is failings with reuse/maintainability) in Winrunner. Because of this (and some other things I am sure) Robot wasn't considered as robust as Winrunner.
Finally, the Tech Support for Mercury at that time was far far better than SQA/Rational/IBM. And that was a major selling point for people. But now with the way Merc. support is going the playing field is getting leveled.
These are my observations/opinions from working with these tools (and others) over the last 17 years. I remember Robot when it was 1.0 & owned by SQA.