The answer is going to depend on your definition of "survival".
Many small groups have the ability to survive based on being able to move quickly to avoid danger and take advantage of opportunities. They also need fewer resources overall, so can take advantage of may more places (a tiny valley might feed a "tribe" of 30 people, but not 100, for example).
OTOH, small groups lack the manpower to carry out large and complex tasks, and can only retain a limited number of skill sets. They will rapidly descend into a neolithic hunter-gatherer lifestyle.
A large group has the issue of stripping the area of available resources, and not being readily able to avoid danger or move to take advantage of opportunities (look at refugee columns in the modern world trying to flee a war zone for some organized camp). They will have to choose their settlement area wisely in order to maximize the resources available, and sustain their numbers.
Unlike the foraging tribes, however, they do have the manpower to undertake larger tasks to improve their lives. Building dams, irrigation ditches, defensive walls, sheep pens and agricultural terraces are all much easier when you have a lot of people to do the work, and more people to support the workers (everything from cooks to medics and blacksmiths). Large groups also have much broader and deeper skill sets, and the loss of a single individual isn't going to be a disaster in terms of losing knowledge. It is actually thought that the Neanderthals, living in much smaller groups than Homo Sapiens, were driven to extinction because of this factor (the loss of a single individual might mean the only tool maker or herbalist in the group is gone, and the group starves to death being unable to find, train or recruit a new one in time). If a Neanderthal with critical knowledge died in the middle of winter, the neighbouring Homo Sapiens in the next valley might not even be aware of what happened until spring.