I used to own a Lowepro Mini Trekker, must admit that the interior is quite well planned and easy to access your equipments. But I find the padding quite thin and soft. Of course the design of the bag is quite....erm....ordinary/dull......basically no design.
After using it for half a year, I sold it and bought a Crumpler Shrinkle backpack and a Crumpler 6 Million Dollar Home slingbag. While the Shrinkle backpack is quite difficult to access, but at least it offers lots of security. And the padding is much thicker and harder. It also allows you to carry a laptop in a seperate compartments. I feel that the Crumpler backpack seats more comfortably on your shoulder. The main plus point of Crumpler of course would be the design. If you often do shooting out in the city, then Crumpler is the bag for you to blend into the crowd. But if you are a nature photographer, then I think Lowepro would be a better choice.
Btw, my Crumpler bag is black in colour, so it doesn't really attract any attention. If you don't mind attention, then by all means choose the colourful ones.