OK, top-view tubes.
Burroughs tubes are my absolute favorites for their quality and reliability. Even tubes over 50 years old look great.
5092's are frequently available on ebay; there are usually some available as buy-it-now at a higher price. Sockets are readily available.
6091's have the same electrical & mechanical pinout, and are larger. I rarely see them on ebay, except 2 weeks ago there were 2 of them.
Avoid 5031/5032 tubes; they are not nearly as reliable. I believe those are earlier production models, though they have the same pinout as 5092's.
And by all means, stay away from IN-1 nixies. They are larger, cheaper, and readily available. I tried some in a project last year and I would get a failure every few days (my big clock has 15 tubes)