global variables for gui

hello to all kind scientists I want to alter cdata property of my buttons such that pressing some buttons may lead to alter cdata of other buttons cdata contains printed image on the buttons. i have three solution and i can not execute all i want to know which way is the most competitive and swiftest?

1.i can use global method to share all pictures:

 global imread('pic1.png)

2.or use handle property

 handels.pic1=imread('pic1.png');
 guidata(hObject, handles);

3.or call every images when usage in pushbutton callbacks