I have a Honda Civic CX with 157K.
The oil filter cap on the valve cover states 5w30 but this car is 15yrs old now.
Been running Castrol GTX or Penzoil (only a few oil changes) Conventional 10w30 since I got it in 06.
Just switched to Castrol GTX High Mileage 10w40 due to it being summer time. I'll go back to 10w30 after summer.
So the question is what are you running in your daily and why?

 

Currently running 10w-30 in my '97 LX. Mine has a leaky valve seal or two, and until I can get it fixed, the engine seems to like the 10 weight better at startup (much less smoke than with the 5). But I keep it at 30 since my engine runs normally all year (never gets above 206*, according to the Scanguage).

Once I finally get around to replacing the valve seals, I'll probably run 5W-30 Mobil 1 synthetic.

 

I'm running 5W-30 conventional oil. Right now my Gen 6 Civics have Mobile Super (5000) mainly because it was on sale. If I could afford synthetic oil I'd seriously consider using it.

For a good discussion of oil viscosity and conventional vs synthetic oils see this ten chapter mini book at Bob the Oil Guy. One take home message is that it is better to run a 0-30 or 5-30 than a 10-30. Less wear on start up, which is when most wear occurs.