I've only been doing this for a couple years, so I'm no expert, but there are a few things I'm very much convinced of:
1) TBHs are definitely cheaper. The last Lang deep super I bought, purchased from a local supplier, cost me over $50 including frames and foundation. It would be a bit cheaper online, but then you'd have to pay shipping and you'd be up to almost $50 anyway. That's just for a single deep super. My TBH cost about that to build, but there will be no additional cost for more supers/frames, bottom boards, top covers, inner covers, queen excluders, etc. etc. What's more, you won't need an extractor.
2) Bees seem to like building natural comb more than they like drawing out foundation. I've been replacing some frames in my Langs with frames consisting only of a starter strip. So I have starter-only frames sitting right next to regular frames with foundation. In every case thus far, the bees have built new comb on the starter strips before drawing out the foundation!
3) I have to agree with Cozy that there's more opportunity to paint a TBH than a Lang. My daughter has hers painted colorfully all over with pictures of bees and Peace symbols! It would be hard to get any sort of artistic thing going on a Lang when supers are always going on and coming off...
4) Using a digital camera, you can do a pretty good inspection of the hive with minimal disturbance to the bees. Just pull a few top bars off in an area where they aren't very active, and stick the camera down inside! Most cameras can do video as well as pictures, so you can easily record what's going on in there.
5) Bees seem to be less aggressive, but I can't say for sure because it's possible that I simply have a gentle colony in the TBH.
6) The only thing that I don't like about the TBH is that they stick comb to the sides, making the bars difficult to remove without damage.
Just my 2 cents.