In general I'd suggest the 1st over the 7th, so if you're also hearing better reviews about the more central hotel, I think it makes for a no-brainer to book that one. Staying in the 7th is fine, and there are people that prefer it, but it wouldn't be my personal preference. It's still relatively "far" from other tourist destinations and lacks some of the charm of the older/more central arrondissements. That being said, it depends on what other sites you intend to visit on your trip, and personal preferences. The 7th contains many sites that might interest you specifically, particularly if you're into Napoleon or military history, and will be calmer and more residential than the 1st. I think you'll be fine in either, so the choice really comes down to what you plan to do during your trip. Maybe map out your must-sees on google maps and then decide which hotel makes more sense based on those.