Estonia and Latvia in March. Any suggestions on where to stay, that to not miss, how to travel, eg rent a car

I've only been to Riga, but its a great city and i really enjoyed it. We stayed at a hostel called fun friendly franks, which was great - it lives up to its name! The occupation museum gives you a good understanding of the history of the area. Public transport in the area is really cheap so you might not need to rent a car.