2 days - Helsinki or Helsinki and Tallin?

I haven't been to Tallin, but for me, one day in Helsinki was quite sufficient (not because it's a horrible place, but an uninspiring one). Others, obviously, disagree.

I don't agree with Harold about Helsinki. I think it is a lovely and interesting city.

I have also been to Tallinn, and it is one of my favorite places I've visited in Europe.

The good news is that while you could easily enjoy spending two days in either city, you could do them both justice in a single day.

I assume you have to get to Helsinki because that's where you're flying out of? If so, keep in mind that the ferry crossing from Tallinn to Helsinki is just 2 to 2.5 hours, and there are numerous daily sailings, so you wouldn't have to commit to a specific time to do that crossing. So if you're in Tallinn and loving it as much as I did, you could wait for a later ferry. Or if you want to go sooner and have more time in Helsinki, that would work too.

We are in Helsinki now after spending tne last two days in Tallin. Helsinki is nice enough and there are some enjoyable things to see, but personally I prefer the old town of Tallin.
I'd skip Helsinki entirely and spend 2 days in Tallimy .02

I only went to Helskinki and enjoyed a full day there (I especially always like a good open-air folk museum, if you have not already maxed out on those) but have since regretted not adding time for Tallinn, when I was so close.

+1 on what Laura said. I recently took Silja Line from Stockholm to Helsinki. While the stop in Helsinki was great, I wish I had added Talinn to the itinerary. It would have been fairly easy to pull off. I remember getting back and seeing Rick's show on Helsinki and Talinn and wishing I could have thought that through more. Either way you win. Helsinki was great.

Tallinn, hands down. Helsinki is ok, but Tallinn is memorable and a place we hope to return to one day.

Tallinn is beautiful. I enthusiastically urge you to include it in your itinerary. I visited as a port stop and was first off the ship to see it before the other tourists, and I think it would be best to overnight there and have time to enjoy the well-preserved medieval town in the mornings and evenings when day-trippers are gone.

Go to both. I have spent a full day in both cities and thoroughly enjoyed both. I'm surprised some people don't like Helsinki. I thought it was fascinating.

We just returned from a month in Scandinavia; retired folks. Helsinki and Tallinn are both worth the two days. The over night ferry from Stockholm to either is an experience in itself.
I would assume you will return some day; pick one and enjoy. Splitting them will require more travel time well spent exploring.
Go out to the fort in Helsinki; a great cave type place to eat with a view of the harbor thrown in. Shop in the "old town" of Tallinn.
Either way you will be happy with your choice.
Papa

We just returned. Spent 9 days in Helsinki with a day trip to Tallin. I think you can't do either in 2 days. The day trip to Tallin was not nearly enough time, the old town is amazing. Helsinki is beautiful as well. Pick one, not both.