the B1 is a quite neutral mic. what goes in comes out. it's good for when i want that. i don't have a pair, but i don't really need a pair.
my 603's are somewhat different. they are sparkly at the high end, which works really well for a mellower guitar, or for where you want the guitar track to shine/sparkle.
i don't have any mc012's to relate to, but my experience with them is that they're typically on the opposite end of what the 603's are.
the B1's do a fine job as long as you're looking for a "neutral/clean" recording of your guitar.
cheers,
wade