I know that FlixBus, which we used to travel from France to northern Spain, operates between the Baltic capitals. My question: do tickets need to be reserved in advance?

We used Lux Express last year to travel between Tallin, RIga & Vilnius. We reserved in advance because we wanted to get the more spacious lounge seats. I remember the buses being pretty full so I would book in advance if you can.

Good to know. Any other recommendations for those three cities?

For the bus be sure to bring wired headphones, They have a ton of movies to watch. Keep your passport handy as the bus stopped at the border of Lithuania and the border partol got on & checked everyone's passports. And bring hand sanitizer as there is a toilet on the bus but no water to wash your hands (though the sign indicated there should have been).

Are you doing a day trip to Helsinki form Tallinn? We really loved Helsinki.

And are you interested in restaurant recs? I can check my notes.

There are several bus companies and lots of seats, so booking in advance isn't essentia. But if you want a specific bus, especially the Lux Express lounge seats, book ahead. Why not go online NOW and see what's available this afternoon or tomorrow? That will give you an idea.

You can now also travel between the 3 capitals by train: https://www.seat61.com/trains-and-ro...n-by-train.htm

We are staying multiple days in each capital starting in Tallinn and flying home from Vilnius.

For all three (Tallinn, Riga & Vilnius) Bolt (their version of Uber) was easy to use and cheap. We used public transport a ton but went to some restaurants and things that were easier to get to via Bolt.
Everyone spoke English. We had prepared the usual words (please, thank you and so on) and everyone just spoke English to us. All the restaurant menus also had English
In general things got cheaper the further south you went- Riga is cheaper than Tallinn and Vilnius is cheaper then both of them.

I assume you know all the major sites so I'll just highlight a few things you might not have come across.

Tallinn
The Tallinn card was a good value for us. It was pretty rainy so it let us pop into places we wouldn't normally have visited just to get out of the rain for a bit.
Make sure to check out the Danse Macabre displayed in St. Nicholas Church & Museum
Balti Jaama Turg- market/food stalls downstairs but we enjoyed the antique/flea market area upstairs. It’s near the Telliskivi area which is great for street art (which I love)
As mentioned Helsinki is a great day trip (though we stayed for a few days). The ferries that connect the two are like giant shopping malls. Very comfortable.


Riga
We used the trams a lot and got 3 day passes from a Narvesen store (like a convenience store/mini mart)
The view from St Peters is really great
Architecture is my husband's thing so we were all over the city. Tons of art nouveau

Kaunas- if you have the time Kaunas is a great day trip from Vilnius. We actually stayed 2 nights.

Vilnius
We stayed at AirBnB apartments the whole trip. The one we booked in Vilnius though smelled of smoke & was dark & dank so we got a room last minute at Hotel Vilnia. It turned out to be a great spot. Comfy beds and a good breakfast was included. Very happy with the stay. I think they were someonwhat recently opened.
The view from the Campanile of St. John’s Church is great (can you tell we like views?)
Church of Sts. Peter and Paul- we took a Bolt here but I think there is a bus as well. It's outside of the main tourist area but worth a visit if you like Baroque churches. Lots of stucco ornamentation.
Open Gallery- if you enjoy street art this is a good spot. We took a Bolt. It’s a working factory/warehouse area that they invited artists in to paint.
Amber is a specialty of Lithuania (though you’ll see amber shops in Riga & Tallinn it is not actually from either of those countries). I bought a really nice necklace for a gift at Etelli Modern Amber.
Local House Amatų namai & Galerija 16 are two shops that sell locally made gifts and art that are worth checking out

Food- we always like to eat the local/traditional food when we travel but I had a hard time finding spots in Tallinn & Riga. Local Reddit users basically made it sound like a combo of- we don’t have our own local food because so many other countries ruled us over the years so what we have is actually from them and what we do have we eat at home so we don't want to eat it in restaurants because eating out is expensive. I don't know how accurate that is but I know I had a hard time finding good traditional spots. So for those cities it wasn’t really traditional food.
Vilnius was a bit different. We were able to eat some traditional dishes there which was great.

Tallinn
RADO- We had lunch here twice because we liked it so much. They write the menu each day on the board. The picanha seems to always be available though (and is excellent). It’s right in the old town area.

Osteria Moderna Itaalia Restoran- in a more residential area outside of the old town. Very good Italian.

Restaurant Mantel & Korsten- also outside of the old town. It’s in a nice old house.The yuzu tart was a stand-out.

Riga
Italissimo- Italian, excellent food & service, my husband’s favorite spot on the trip. Definitely popular with locals. The place was packed on a Monday night.

DOM- surprisingly good for its location and the cutsey Instagram ready paint job on the outside. We had lunch here twice. Service was good the first day and just ok the second.

Pētergailis- nice spot, good service. I liked it more than my husband

Gauja- a bit of a hipster spot but there were all kinds there eating. Had a great secluded outside area. They offered two mains for lunch plus the option to add soup (I think). Very affordable and good.

Vilnius
Georgian House- Georgian restaurant, good spot right by the old Jewish area, Nice outside and a good lunch special.

Bazilijonai- just outside the old city gate this spot serves traditional food like cepelinai (football shaped potato dumplings filled with ground meat) as well as non-traditional food like beef cheeks. Not fancy and by far the cheapest spot we ate at for dinner. We also tried the kepta duona (fried garlic smeared bread with cheese dip). All very good.

Hope this helps!

I'm not the OP, but thank you valgalchi for all the information - it will be useful to us, as well. We are visiting Tallinn and Riga in July (along with Helsinki). I've been to both briefly, but 20 years ago. I also liked Vilnius on that trip, but we're saving a return for when we have more time. I have ancestry from that area and need to do some research first!

This has become part of our travel information. Thanks.

ms_go & Michael, glad this is helpful!

ms_go, I posted some restaurants for Helsinki on another thread. We really enjoyed the food in Helsinki. If street art is of interest the Pasila area has a ton. And I also have Lithuanian heritage! That's mainly why we added Kaunas, to get a bit more of a feel for the country. But there is lots more to see for sure!