At present, mostly IDPA with a dash of IPSC and USPSA.
I shot F -T/R class up until The Incident of 2010 but am now so far behind the curve that I doubt I will get back into it.
I also shot BPCR for several years. Been invited to fire up the Browning and get the Winchester adjusted for another pass at that.
In the past I have shot smallbore, PPC, CAS, ATA, CMP RFS, probably some others.
Mainly, as Mark says, the key is the scorecard and the competitors.
If a coworker had not gotten me into Trap a couple years after I got out of college and could afford ammo, I would have gotten tired of solitary vice and taken up one of those sports with the ball that Thomas Jefferson said inferior to the gun.