I need to tile a shower stall, I have removed the old tile and sheet rock, and yes it was sheet rock, the house was built in 1969. My question is what do folks recommend, green board or cement backer board.

Both are considered acceptable but I go with cement board or Hardibacker. Inspect your framing closely to insure you don't have mold already growing behind the drywall, wouldn't you just kick the guy who did this?

Greenboard is no long up to code. Use the CB/Hardibacker with real thinset - dry mix, not premixed. Same with the grout - do not use premixed. You should also use a vapor barrier behind the cement board, but if there is no mold now, you could probably get away without one.

The fun thing about hardi-backer joining to sheetrock is that a fair amount of sheetrock is 5/8" thick, but most cement boards come in 1/2" or 1/4" thicknesses.

If your sheetrock is 1/2" you can ignore the rest of this.

You may consider the greenrock to come level with the existing sheetrock and then use 1/4" hardi-backer over the greenrock. You would then need to use a "bull nose" tile to cover the edges of the hardi-backer. Bull nosed tiles are designed to handle the 1/4" ridge.

Was Lynch mistaken about greenboard no longer code? The thickness differences are that much of an issue when you've torn out the wall. We just use the same thickness drywall above the Hardibacker as the backer we installed.