My last boat had both AIS and Radar. The most useful is definitely the Radar. Yes if you're offshore commercial shipping will show up on AIS but both commercial and private boats will show up on the radar. My current boat has Radar only, I have it on most days when travelling just to keep used to using it, also I think if you have navigational aids you are supposed to use them. I don't go out in fog intentionally however I have been caught out with near nil or very close visibility mid channel the piece of kit I would rather have is yep you guessed it Radar as it will see you safe from well offshore to inshore where most small craft don't have AIS. Don't get me wrong AIS is brilliant and I have been called up by name by commercial shipping asking my intentions so from that perspective it is useful just not as useful as Radar. If you can afford both then have both if not radar is the thing to have
Get radar do a course and use it, learn how to adjust manually without relying on auto settings which are ok but just not as good as using the correct settings.