The 220+ was the first model I had, I found this slow and didn't natively support docker as part of the package manager. Docker compatibility should be a priority when buying if delving into some setups mentioned here it just makes everything so much more convenient. The 16 series model is expensive to buy new, I picked mine up used from eBay from someone who was upgrading to a newer model. You can Google Docker compatibility for Synology models and get a list of models that work with it and narrow your choices down to these.