Hi and welcome! What size are you thinking? We usually go with the three small "hardiest" ones being the Russians, The Greeks, and the Hermans. Going up in size we say the Cherryhead/redfooted tortoise, even bigger would be the leopard and sulcata. Keep in mind you need to also look at where you live, how much time and energy you want to invest in the tortoise and it's habitat, and then there is money not only for the tortoise, it's food, it's Vet bills, but also those enclousres do not come cheap. The sulcata especially can be a challenge once it gets bigger and it starts thinking it can go through walls or dig under things. Also an adult tortoise is normally much more hardy then a hatchling.
As Jacqui said, if you want hardy, go with an adult. Hatchlings can be challenging and are more difficult to keep alive.
Different tort species have evolved to fit different ecological niches. So, hardiness of a tortoise will depend on the environment its kept. What are the temps and humidity like where you live? Do you have long or short winters? Do you have snowy, rainy, or dry winters? Do you have hot or mild summers? This information will all help you determine which tort species will be hardiest where you live. Tortoises tend to do best when kept outside (weather permitting). How much outdoor space to you have to keep a tortoise? 5x5ft? 10x10ft? An entire backyard? Some species need much more space than others.