do any of them work well??

I use prolong, been using it for years I know it works. no I won't admit how I know either  

I personally don't use any oil additives, especially after all the stuff I've read about additives clogging oil passages and filters.

My favorite additive;
    conventional oil.

Without it, you won't get very far.
~Nate

once you use prolong, your cylinders cant be overbored, because the oil seeps into the pores, or something to that extreeme. but once your engine is worn in PROPERLY, run prolong.   A regular oilchange however will do just as much, rememnber,
"Oils cheap, engines aint" - Roger Niles, Automotive teacher

this is true.......

I personally don't use any oil additives, especially after all the stuff I've read about additives clogging oil passages and filters.

Me too and I've heard the same  thing.