Group Ride or Group Run

Group ride.  Miles seem to go faster, conversations are easier, get used to a group running dynamic (which you will have sort of in most triathlons, especially an IM).

Just my opinion.

My long runs are meditative for me and I prefer them at my own pace.

Long rides can be tough in the Winter. I'd never to rarely get out for long Winter rides if I didn't have company. Unlike running, it's also a little easier for people of somewhat different abilities to get the workout they want (someone needing more of a workout can pull longer in front and push hard up the hills, for example).

From what I recall you saying your running club most folks aren't same pace as you, so why run with them?

Cycling with others of similar ability is wonderful. I tell my friends when I ride with them it is like a gift..doing something I love with friends nothing beats it. Of my miles I do less than 3% with others so each group ride is special.

I'm doing 50ish Sunday down on the Cape with friends..can't wait! 

Group ride helps with your handling skills, communication and allows you to go faster than you would by yourself.  It allows your body to benefit from several things.

Group run, it's just about running with someone.  Granted, you can push yourself harder, but when you blow, you blow.  Group ride, you can sit in and hold on when you blow and still get some benefit.