Upvote:4
I made this journey in 2017 and took the overnight train from Tbilisi to Yerevan. It cost approx 90 GEL in first class, and less in other classes. It has the advantage of saving you the price of accommodation.
It goes from the main train station in Tbilisi to the main one in Yerevan. Tickets can be bought at the international/long distance counter upstairs in Tbilisi train station.
2 years ago, the train had air conditioning but no Wifi while in Georgia, and Wifi but no air conditioning in Armenia!
Upvote:6
So, from a few sites I was able to get the following information. This one is the most detailed and includes maps and images, this is also a good source.
It has been said to be the cheapest and easiest way, tickets seem to be around 35 GEL but I haven't seen that anywhere official, as you just pay the driver on the bus. (In comparison a flight is more than 100x that much, and a train is at least double). But it does take 5/6 hours depending on holidays, traffic etc.
You can board at Station Square, Ortachala Bus Station, or Avlabari to catch your bus from Tbilisi. They have a Schedule at the first two which they mostly keep to, and the last waits for the bus to fill (sometimes taking hours). This then goes to Central Bus Station in Yerevan. It seems like the bus makes some stops on the way to allow for bathroom breaks/buying food but I couldn't see any official locations stated for where this happens.