From what I see there are two major differences in laser bore sighters, one loads in to the chamber and one loads in to the muzzle. which one's the best?    

I would hope that it's the one that loads into the muzle. The one that loads into the chamber just got me onto paper at 50yds. ( expected more )

I have a cheap chinese one that fits in the bore.  I don't like using it on a good bbl, because it has to be a tight fit to work properly.  In order to make sure the laser axis is aligned with the bore insert, you have to rotate the insert (and laser) in the bore while it is tight.  This will probably cause some damage to the bore.

It is good enough to get me on paper at 100 yds.

OK Thanks guys,

I'm looking at the Boresighters in the Cabelas catalog. Does anyone Know which one of those is the best?

I have a laser boresighter that fits into the chamber.  It’s made by ALPEC, and I purchased it from Brownells.   My experience is similar to that of KZ45, it got me on paper at 25yrds, but was not as exact as I expected.  It is instructive to play with the scope’s controls while having the boresighter turned on, as you can see if the scope/controls track vertically and horizontally as they should.

My laser is not very bright, so I had to use the boresighter indoors.  Lastly, it did not work well with my Aimpoint , as the scope attenuated the laser dot to the point that I could barely see it.  It worked fine with my ACOG and Leo.  Overall it’s a nice device to have available, although once the scope is mounted it doesn’t get used (except by everyone who now borrows mine).