Estonia has been one of my favorite European countries for buying SIM cards and data because its so incredibly cheap! You are already aware of this if you have read my Buying a SIM Card in Estonia Guide.
It would almost be criminal NOT buying an Estonian SIM card and instead opting for connecting to WIFI hotspots. Those can be slow, unreliable, and unsecure.
Plus, with these low prices, you would do yourself a disservice for not buying an Estonian SIM card.
There are 3 operators in Estonia, Elisa Estonia, Telia Estonia, and Tele2 Estonia, but each operator has 2 prepaid sub-brands (Elisa & Zen for Elisa, Super and Simpel for Telia, and Tele2 and Smart for Tele2).
The main difference between the brands is the packages they offer, except for Tele2 and Smart – Smart customers can buy regular Tele2 data packs.
Click on any of the logos to read my review of the said operator, or you could read my Best Prepaid SIM Card in Estonia Comparison, where I compare everything I know about Elisa, Telia, and Tele2 Estonia, and see which operator is the best for certain scenarios.