Jenise,
If the choice is between Reims and Épernay, it would be a no-brainer for me in favour of the former and not just for the trams

. As well as Champagne interest, Reims has one of the finest gothic cathedrals in France, where the French kings used to be crowned, and two reputed up-market restaurants, Le Parc Les Crayères (Michelin 2014 **) and L'Assiette Champenoise (Michelin 2014 ***), and a slightly less up-market Le Millénaire (Michelin 2014 *).
If you prefer to be out of town, we have enjoyed our stay a couple of times at La Briqueterie at Vinay, 6km from Épernay with a good restaurant (Michelin 2014 *). Many years ago

(for our 20th wedding anniversary) we stayed at a very nice château/hotel in the Champagne countryside but, so far in my Michelin and Google searches, I can't identify it so it may no longer exist. If I locate it and it still sounds good, I'll post again.
If you have time, do try to visit some smaller (Récoltant Manipulant) producers. For access to them, Épernay is more central. I particularly like Pierre Gimonnet (Cuis), Pierre Moncuit (Le Mesnil), Gatinois (Aÿ), Larmandier-Bernier (Vertus) and Egly-Ouriet (Ambonnay); the last is becoming pricey and cultish but wonderful still red Coteaux Champenois Ambonnay. David can probably suggest many more.
Apologies for quoting from Michelin 2014 but I don't have a more recent edition.
PS: I think that the place in the country where we stayed in 1990 was Château de Fère at Fère-en-Tardenois
http://www.chateaudefere.com/fr/ . It looks grander than when we were there and has lost its Michelin stars. It is also 50km to the west of Reims and therefore quite off-centre if visiting core Champagne wine villages.