I like them, and use them all the time, but they are far from perfect.
I'm curious as to what you don't like about them (other than wanting a bigger one). Personally, I'd like a pair of Sliplock attachments like the older version had vs. the one of the current versions, but other than that, they're pretty much ideal.
For me, no need for a bigger version - the 75 AW holds a 1-series body with L-bracket and a large white zoom (28-300L, 70-200L II, 100-400L). In fact, it holds my 1D X with the 100-400L and a 1.4xIII TC attached (so I suspect it would hold a 300/4L IS, too, but not with the TC). The only need I could see for a bigger one would be to hold the 400/5.6 - but I don't have one and have no interest in getting one...