Few points
1. We generally make versions widely recommended upon wide adoption in order to help customers make this choice. The recommendations can be found in sk95746
2. Right now the best fit wide choice is R80.40
3. R81 has been out for quite some time and is definitely widely recommended for management versions (we have very large adoption of Smart Center and multi domain). R81 is excellent choice for management
R81 GW also have good usage but we havent made it yet widely recommended as all its GW quality improvements are also released into R80.40 and we were careful sending a message that customers should prefer R81 GW on top of R80.40 GW. We want to save unnecessary movement.
There is internal discussion on the communication next step and commentary is welcome
4. So if I install or upgrade now, I definitely use R81 management and I would decide on the GW based on functionality. If I plan to use new GW feature in the near future, I would go with R81 but if not, I would take the most widely adopted GW and that is R80.40