I use Ernie Ball super slinky -- 0.009 - 0.042. Have used them for years but can't say I put much thought or effort or scientific experimentation into the decision other than that 0.009's were easier to play than 0.010's. Didn't choose Ernie Ball over others for any reason at all, totally arbitrary.
Would be interesting to hear the thought process of anyone whose chosen a particular brand of 0.009's due to some actual, more or less "scientific" experimentation.
I notice I break the 0.24W string most often, and that's on all my electric guitars, (of which I have 13, so it's not just that bridge saddle on one guitar or something.) After that, it's probably the 0.009 string I break 2nd most often.