Ball joints are neat, particularly the new Hero Factory ones. They aren't particularly strong though.
The amount of squeezery put out by the hand-clips is much smaller than the tile-modified ones.
You can see how I was doing it here
. It looks like the first image has bitrotted away, but you can see the knees in lower images. I use a lot of pneumatic Ts but taps are a much cheaper alternative.
You're also going for a shape of leg that doesn't exist in nature. I recommend going to the master (evolution) if you want something to work well and look "right".
Dig the feet, btw.