I bounce back and forth as well. I'll run a patrol in SH3/GWX 3, then go over to SH4/TMO/RSRD. Now that I'm delving into manual targeting, I'm realizing that the methods both countries used are completely different beasts.
Plus, when I begin to suffer burnout, I'll fire up either Fallout 3 or one of the Elder Scrolls games. But other than those, that's about all I play now.