Now then... this isn't intended to discuss which is better as there has to be merits to both or all of us would have the same manufacturer.
What do you go for Shimano or Sram? Or do you have some of each on different bikes?
My personal choice... Sram drivetrain (shifters mechs and cassette and chain) with shimano chainset and brakes on all of my bikes..
Why? I prefer the shifting action on sram (slightly more industrial feel but feels more solid in my opinion), I think shimano offers better value for money on the chainsets though and really like the clearance in shimano brakes even if they are a bit on/off so run these for ease of set up and lack of rub.