I had got an offer from a company X 2 months back. Though the compensation was pretty good, I asked for more. They declined and I continued my search for the best. I was expecting good companies (Y, Z) will contact me, but that din't happen.

Then 2 months later, now I re-approached company X again and they issued me the same offer. I accepted it, resigned from my current company and serving the notice period (2 months).

Now the twist: I got calls from Y and Z (good companies). They definitely give better compensation. If they select me then my plan is to accept the better offer from Y/Z and inform the X immediately that I have got better opportunity, so I will not be able to join the company...

Is this ethical ?

[Edit Note: I have to just send an acceptance email (i.e. no contract signing) which doesn't legally bind me to join that company. So, legally I am not doing anything wrong. However, I am worried that if I am doing right/wrong ethically.]