Heading to Arugam bay is by far the best spot for digital nomads !! There's so much to do and the wifi is not that bad I think. It's a great gateway from the big cities: surfing, elephant, beautiful beaches and great coffee & bars
It's as good as Changgu in Bali in my opinion.
There's also Ella where you can have a spiritual retreat, nice foods and great hiking in the surroundings. Don't expect too much from the weather but at least you get to be far from the highly touristy spots.
Last but not least, kandy is way bigger than the other two cities. They say it's the cultural city and you can get some more "city stuff" like clothes.
PS: arugam bay have the best falafel I've ever eaten in my life so far!!!