i agree with everyone.
stay or leave. since you have better offer, just let your boss know about it and tell him the reason u leave like a gentleman. there're no hard feelings when comes to work. tat's what i told my staff, if u r not happy working,let the management know and if the problem still cont and u have better offer, let us know n prepare. fair for u fair for us.
i'm too facing problem like ur current company. train them n they leave; get better offer from what we've produced them. but that's life; i do have loyal staff for more then 5 years which they have LOVED the company but new freshies always seek for big $$$ rather then exposure. so it's either you want to gain better expirience in your field of intreast career or to get high $$$. some leave for better career some leave for better $$$. at a working level, you must love and enjoy what u r doing.. that's abt it