Any reason to book this ahead of time? We have to take an AM ferry from Hels --> Tallinn on June 16 .
The ferry is enormous and not likely to sell out, but I did book my ticket (early Sept) ahead of time on the Tallink Silja Line website, very easy. I'm the kind of person who prefers to have everything lined up.
Yes, I went ahead and booked myself as well! bon voyage.
There are three ferry companies operating almost hourly service on this route: Viking Line, Tallink and Eckerö.
Currently the best product (on-board experience, shopping, dining and entertainment) is on Tallink's Europa and Tallink's Megastar, the latter one was built in 2016.
Both Viking and Tallink also offer a kind of overnight ferry on the route. Tallink's Europa and Viking's XPRS depart Helsinki in the evening, arrive in Tallinn just before midnight and you can sleep on board in cabins just like in a hotel until the next morning. Depending on the season this can be a cheaper option than staying at a hotel landside.