i typically use the filter w/ qlink afterwards to control the expression of the sound, not necessarily to create a new sound. that said i have no real issue with how the filters sound in the mpc - listen to the opening of my track "the sickness" to hear how ground tremblingly hot they can be (headphones or subwoofer are a prerequisite for this one)
ALSO, i only ever use the lowpass filter, reallly...occasionally others (like in Divining Rod, one of the songs i posted in this thread earlier)
http://nymantics.com/thesickness.mp3 <= heavy use of the mpc1000 low pass filter throughout. lends a somewhat eerie movement to the lead sample.
these days, if i'm after a different filter sound, i use Ohmforce's Frohmage freeware filter plugin - by far my favorite filter plugin i've ever used, and it's free. an incredibly enticing warm sound - i'm not one to use the "low end theory" when sampling from records, but if i were, i'd use this one because it's just lovely.
the mpc filters to me are more just raw dogs. they are what they are - i don't use em on my record samples (rarely, anyway) and when i do i often replace it in my final mixdown with frohmage just on principle.