Red line. Bmw approves it for constant use. People think that the detergents in gas are enough, but a few companies(gm comes to mind) are complaining that customers still see build-up with ALL brands of gasoline. It provides an upper cylinder lube as well as a few other benefits. Been using it in my truck since I got it.
Is it going to be used full-time? If it is then I wouldn't recommend anything but Red Line (at the 100 gal. dilution). Not saying there aren't other suitable products, just none that I'm aware of. Not that BMW is the end all/be all (usually they know what they are talking about though), but they also say Chevron-techron is safe to use (and effective), but only twice per oil change (they have much longer oil changes than we do, fwiw). It builds-up in the oil and can harm the motor, supposedly, if used more than that.
I thought seafoam was just poured into the throttle body/carb (i think they also have a spray), do they also have a fuel treament? I've heard that it's good stuff though.
I prefer the spray "Deep Creep" for throttle bodies and carburetors, and Sea Foam for the gas and crankcase.
It says its good for diesels, but I recommend the Lucas fuel treatment PN 10003, 10009 for diesels. Power Service makes a great product for diesels as well, but again, the viscosity is not there in the PS products.