Bragging about previous funded PhD position to acquire another? I am in the process of leaving a funded PhD position and apply elsewhere. There was a lot of competition for the position, and the benefits were good (being employed by the university), but things didn't work out (mainly I want to pursue research that is not being done in my first university).

Could it be useful to brag about how I got a competetive PhD position in my application to other places? My first university is not famous, but I did come in the top 5% of over hundred applicants.
This is just an opinion:

You will need to be very clear why you left, and you cannot leave room for the suggestion that it was just because things got a bit uninteresting. The way you have described it in your question leaves me with that presumption, and on that basis I would feel uncomfortable with working with you on a fixed term (or fixed goal) project such as a PhD.

i.e., the obvious question in the mind of the reader of your CV will be, "How do I know you won't disappear on me as soon as things get a bit boring or difficult?"

Frankly, I think you have more to lose than you have to gain by discussing it.