What automation tool for testing web application can you recommend to beginners? Which one is better to start with? I have no automation testing experience.
"Most appropriate" is the one that best meets your company's individual needs.
It depends on the technology, but also the budget, the time available, the knowledge and capacity of the individual(s) who will be using the tool, etc, etc. No one size fits all.
Here is a list of vendors that have trial versions you might choose to explore. Not only will this give you some exposure to the tools available, but it will also help you understand which capabilities are important to your individual situation:
I use WinTask. It meets my needs at this time, but it might or might not meet yours.
Here is what I look for in general terms when I put together a suite of automated test tools. You might find it handy: