I will be in Paris the week of March 12-17 and am planning a day trip to Reims. Do I need advance train reservations? Any suggestions on which champagne tour is the best?
Yes, you will need advance reservations since this is a TGV train which requires seat reservations. We only went to Taittinger, but it was a very good tour.
I would also recommend visiting the Notre Dame church in Reims as it is stunning -- and most of the French kings were crowned there -- and so much less crowded than the Paris Notre Dame.
Over the years we have gone to most of the champagne houses- many more than a few times. Mumm and Moet & Chandon seem to be the most experienced at doing Champagne tours and their tours are very organized and interesting. (Including opening champagne bottles with a saber). Bollinger also made us feel welcome, they seem cozier and more family. The one that disappointed most was Laurent Perrier- their guides seemed more interested in talking among themselves. the "plum" would be to get in at one of the very small growers. But i am not sure how organized they would be. (I've only done that as part of a professional group). The cathedral is really worth the visit
Just returned from a month in Paris and went to Reims twice on the TGV. We had a France Railpass but had to make reservations. Since it was low season, we could make them just a few days in advance. I don't know about March, when things in Europe begin to pick up again.
We went on the Tattinger tour and liked it.
TGV trains do require reservations, but they don't usually sell out in advance (except for a few very popular trains, like through trains between Lille and the South on summer weekends) and it's usually perfectly OK to buy a ticket and reservation at the time you want to travel. You can often get much cheaper tickets if you book in advance, but that ties you to a single train each way.