this summer our vacation will end in Rothenburg, but we will be flying out of Frankfurt airport. so far all i can find is train service from Rothenburg to Steinach to Wurzburg to Frankfurt airport. my questions are,is there anything better? more reliable?, because we don't want to miss our afternoon flight home.
Rothenburg to Steinach to Würzurg to Frankfurt. No, that's pretty much the way you have to go. You could go from Rothenburg to Weikersheim to Osterburken to Mannheim to Frankfurt, but that would take more time. (Or maybe Rothenburg to Munich to Moscow to Peking to NYC to Frankfurt. Nah.)
If the train schedule says they will get you there for the afternoon flight, that's about as reliable as you can get.
If you want more reliability, go the day before to Frankfurt or (Mainz).
I would go the day before also. One never knows if there will be an unexpected delay, like a strike, or accident. People have a bad habit of throwing themselves in front of trains as a way of saying Good bye, and this jams up the tracks for hours as you can imagine. Not something I would want to have happen any time, but especially not on a day when I have a flight. Reduce your stress and come a day earlier as Lee suggested.