if you are using the Tor browser, it seems you get one fixed entry guard for several months now. This seems to make some sense:
However, I wonder if having a fixed entry guard is advisable even if you route your traffic through a VPN (like Air) first and then through the Tor network (Tor over VPN).
My guess is that in this case, having a new entry server every every time would makes more sense, since the entry server is less important, and using the same one every time could help someone to track you down.
What do you you think?
(If you are using Tor browser, it’s not too difficult to make sure that a new entry node is selected every time you connect to the Tor network. I can describe a simple option if this is wished.)