I'm fairly new on here as well, best thing is to look at The Events tag and see what type of event or run you fancy.
We did The Surrey Run that was a good mix of all MG's, never been on a run before where you have to follow a map and distances covered. Was a bit of a quick learning curve, but enjoyable and we cheated by following others that knew what they were doing.
Other runs were through the tunnels near Shoreham Airport, good laugh, just MGF/TF's and a Mini a BINI by the way. Good day out nice crowd and a great meal at the Airport.
Best one for me was the Stonehenge run, great countryside, Stonehenge and Avebury, via The White Horse, thats the one on the hill not the pub!! We did end up at The George, Avebury. Again great crowd, lovely pub and as a newbie made to feel welcome.
We have been to the last 4, Pride of Longbridge, again great day out, park up with your mates. We meet up at Hopwood Services and convoy in, bit difficult to park up if you drive in on your own.
So if it were me I'd pick a run, that goes to a interesting location and ends with a meal, so you can chat. I'd book a Stonehenge type one now, as it was well run, interesting stops and time to chat and get to know people.