I love the xperia z1 because of its sexy looks and waterproof proff and dust proof qualities. The phone pack a snapdragon 800 processor, which gives it rocket speed.
Sony has recently provided android lollipop update and its amazing with improvement in the 21 mp photo quality.
And overall no lag because of android lollipop being less resource hungry. The phone is light weight and slim, everyone will ask you about your phone. So this is a good phone but keep in mind it is little delicate.