Technically they are pretty similar - the DAZ generation four figures use a system to add additional morphs that requires running a batch file on installation, but there aren't many things that require that and it doesn't affect day-to-day use. The differences are more in the execution, and in what add-ons have been made for them. I would suggest playing with the figures you already have for a while, and only start looking at additional figures when you start wanting to expand your range - at which point you should have a better idea of what concerns you, and what is just a side-issue.