I know some of you hate to answer this question.
First of all XD100 is out of the question right now. I understand it appears to be the best oil on the market, but I can't get it for less $45 gallon and have to drive 60 miles. Might be worth it if I set my E-TEC to XD100, but I have no intentions of doing that, so I will leave it at the TCW-3 setting.
With that said, if you had to choose would you run XD50 or Pennz full synthetic. Both are within $2 of each other and the Pennz is more readily available.
I can get the Pennz for about $23 and drive 13 miles or get the XD50 for $21 and drive 60 miles.
Once again don't come off with that mess about "well if you can afford the rig then you can afford the oil" you may can, but I can't, argument settled.