I have been using Dean Markley Blue Steel 8's and 9's (mostly 8's)since mid 90's
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Blue Steel strings are cryogenically frozen with a blast of liquid nitrogen. But why would we do such a thing? By freezing our strings down to -320ºF, we tighten the molecules, minimizing microscopic gaps. This process removes transient frequencies that produce harsh highs and muddy lows, creating a more consistent string, with true tone and longer life. A method to our madness!

Made of 8% nickel-plated steel outer wrap on tinned Mandolin wire hex-core, Blue Steel strings have been top-sellers for years and are used by pros worldwide. Once you try Blue Steel strings you’ll be hooked. They feel great, ring true, are durable and long-lasting, and they just plain sound good. (from Dean Markley web page)

IMO the best. I've left them on guitars more than 2 years (on ones I don't play much anymore) and they are still like new It is uncommon for me to break one and I do like bending strings;)

D'Addario XL's came on my Variax and I left them on there so far there ok. not sure what gauge they are...
tried the cobalt didn't like them...
got some black colored DL's for my Six Flags Batman guitar and first time I played them the paint started to fall off.
before I started using the blue steel I mostly used extra slinky or slinky Ernie Ball's but broke offten.