It depends on a few things. If we are talking on road and you are reasonably fit, then a lightweight road bike with compact gearing is the best choice for climbing. But if you are less fit then the much lower gearing on a mountain bike makes climbing easier, but considerably slower. A gravel bike could be a good compromise between the two. They have lower gearing than a road bike and are lighter than mountain bikes. You could also go more old-school with a road touring bike with a triple chainset. Basically plenty of options, but the key points are low gearing and to a lesser extent low weight.