They both have their pros & cons -- yins and yangs to them.
The 4033 may be an electret, but it's still unique in that it's a medium-sized diaphragm -- also 2 microns (or close) if I'm not mistaken -- and is embossed for greater bass response.
Obviously, the smaller diaphragm might mean better off-axis response which might make it a little more versatile. And whatever the hell the embossed diaphragm thing is all about, it really does seem to pack a nice wallup when placed out in front of a kick drum or a bass cab . . . and the SPL handling on that thing is pretty stellar to boot.
From a lot of guys I've talked to, word is the 4040 makes a better vocal mic, and has a smoother top end to it, so in that sense it is apparently an improvement. At the same time, people should know that it's still a very different mic from the 4033 -- and probably has a lot more in common with the 4050 if anything.