How to choose a generalist repository and what risks should I be aware of?
I haven't used any of these resources myself but hopefully the following points can help you in your decision:

This kind of repository and the open science trend in general are pretty recent. This is why it's a bit difficult to evaluate and compare the different options, there's not enough hindsight yet. This is also why, in my opinion, the main risk is that the platform you choose would become obsolete or disappear in the future. So to be safe you might want to choose a platform which allows you to export your stuff easily.

Another important point you should consider is the policy of your institution: the outcomes produced as part of your academic job can be subject to IP restrictions. So it might be a good idea to check with your local IP or legal office what kind of license they allow/recommend and whether there is any IP disclosure process in place. 

It's also worth mentioning that there are a few more generic options for sharing outputs: for instance Github, Google Drive, and of course the good old personal webpage (most universities let you create one under their website).