We've used all the 200X series MXL mics, and found all of them to be pretty crappy. The 990's a cool little mic - it's really a SDC. The 1006 can even be decent. V69ME is very cool - if you don't get one of the noisy ones - as they seemed to have run into some QC problems with that one. 603's a solid budget SDC - same capsule as 990. The V67 - while not being all that great - does offer a chance to get into a darker, very colored mic for pretty cheap.
For vocals and amps, are either of these [ 2001, 990 ] better than the Studio Projects B3?
Well, for one, both the 2001 and 990 are cardioid-only. The B3 will give you cardioid, omni, and figure-8 patterns to play around with. I also think the B3's just a better all-around mic than either the 2001 or 990. Although the 990's still a cool little mic. The B1 and B3 have become well-known and popular budget workhorse mics - but mostly on instruments. While they can work for vocals, that's not their strongest application.
If you're going to get two mics, you're better off getting two mics that complement each other - with each of them having a quality the other doesn't. If you want to go with MXL - and go cheap - you'd be better off getting a colored V67 and a more neutral 990.
If you plan on buying more mics down the road, the B3 would prove the more solid investment in a mic collection, IMO. If you wanna get two mics for cheap - for whatever reason - and stick with those, the V67 and 990 wouldn't be a bad way to go.
My 2¢.