Yeah, different mics have different boosts (usually) at different places in the frequency spectrum, which is one of the things that makes mics sound different. But a big part of the equation is the voice that sings through the mic, too. The Rode NTK is a great sounding mic - I really, really like the sound - but I'm having this sibilance problem with it. Which means the NTK's boost must coincide with or accentuate the natural sibilance in my voice. So, yeah, a flatter mic wouldn't do that, but you'd still have to try out the flatter mic to see if it sounded any good with your voice.
Anyway, since not everybody has this sibilance problem with the NTK, in my case it must have something to do with:
1 my voice
2 the way I enunciate esses
3 mic position
4 my preamp
I can't do anything about #1 or #4 for the moment, so I'm going to continue to work on #2 and #3. I worked at it yesterday and found that if I'm conscious of every ess I sing, it's possible to reduce the attack I give the esses and emphasize the following vowel instead, which seems to help. I'll try recording this afternoon. I'm also going to try cominginsecond's advice about applying de-essing just to the esses in the track.