Kroil has the lowest surface tension of all the penetrating oils that I have used, so it will get into just about anything. I worked at an industrial valve shop for awhile and have seen that stuff free up bolts on sea chest valves that you couldn't even tell there were nuts on for all the rust!
That being said, PB is great too. I have both handy at all times.
Ive used CRC's version of that, which is called Freeze Off! It works pretty good, i think its damn near as good as Kroil (i used it to remove my rusty exhaust manifold bolts), altho i cant think of any product out there that is hands-down better than Kroil. Like BigMikey said, Kroil gets into places it shouldnt. Ive used it to removed bolts that seized into place just from heat (used to work in a foundry) that otherwise just gall & break. Awesome stuff.
I sell PB Blaster and have used it for years before getting a sales job. Now we sell this http://www.gasoila.com/products/items/freeallclassic.html
It is called free all and it works better than blaster. I have never used kroil but I am sure that this stuff is very similar. I sell it cheaper than Blaster so if you can find it where your from it should be a good deal.
Yes, kroil is the best!!!!!!!! It is one of the best gun oils as well. Put that stuff in a dirty bore and it will get under the crude. For stuck, frozen, galled bolts, nuts I have yet to find anything better. Esp since my dad worked a shutdown at a factory and they gave em a can a week to keep thier tools lubed. (some kinda chemical plant). When I run low I raid his shop. Oh yeah, good for fishing reels too! I live on the gulf coast so you have to keep em lubed!