TimeCapsule. Less cable clutter, better drive performance, just a small premium over a AE plus NAS quality drive (you can go cheap on the AE external drive and enclosure but that more like comparing apples and oranges). You can always add an external drive.
I just went through the decision and chose the TC.
If you want, you can swap TC drives. I extended the life of my timecapsule by replacing the drive. Not that difficult, many mod descriptions on line and in YouTube. It is much easier to swap drives in the newer models, many here throw 4TB drives in.
I went from an Airport Extreme to a Time Capsule. The cost of the drive in the new models is quite reasonable and it was plug and play. There is no drive you can plug into the USB port that is going to be any faster over the network than the internal drive.
If can swap drives out if needed on time capsule...then that sounds good.
However... One concern I always have is risk of theft when away....have to leave the router on...but with a TC..all my data would be there for the taking, whilst with an AE+ HD...I can always disengage and lock the drives away....