Birdy for sure over the Reach as a commuter type bike .. 8 tire sizes in 355 from Schwalbe alone .. Reach 451 tires very limited .. also the Birdy folds without removing the front wheel.. since you have to go upstairs frequently, you might look at a Birdy with Capreo hub instead of the dual drive to cut down on weight and complexity and still give you good gear range .. I love the Dual Drive, but I also never had to lug one upstairs .. if you don't need the lowest lows and the highest highs, a Mega-range cassette or Capreo would work..