Out of the 5 shaker cups that I have (cuz ya know, there are 5 days in the week!), all of them are the blender bottles. I've never had them leak on me, and they mix things best of any I've tried.
In my experience, what NOT to look for are the ones that twist on and have the gasket in the lid. The gasket ends up coming out, not going back in right, never sealing up right again, and it's just another place for bacteria to grow if you don't wash it properly.