honestly it doesnt matter where you tap. The numbers are all relative so you just need to know what number to look for that keys you in to trouble. 1600F is no longer the magic number if you tap it in the up-pipe, its more like 1100F or something (i don't know exactly so don't quote me). As long as you know what tempurature you need to look for, you could put it in the muffler with no real ill effects.

however, after saying that, I would say the manifold is still your best bet, as you will only be getting the temp from that cylinder instead of mixing it with the others, but you cant go wrong tapping it anywhere on the drivers side.

or get this to watch both banks . I think i remember seeing one that had 4 readouts too, but i can't find it.