folks, feel free to chime in here....
personally, i am a big fan of the bartolini stuff. i have bartolini's in most of my main basses, with the exception of my passive fenders which are stock. what i like about the bartolini stuff is that is has a growl to it that really sweetens up the midrange and provides great cut if you play aggressively. also, i like the way the frequencies are shelved... the high end isn't too brash, and the bass boost frequencies are quite usable. for the way i play, i just think it's a really musical setup. you can definitely combine different brand pickups and preamps, albeit with varying results... you might find that the mec's may or may not be an optimal combo with the bart preamp... i'm not sure, as i've never tried that combination. with the exception of my mike lull 5 string jazz bass, my other bart preamped basses have bart pickups as well. the mike lull has a bart preamp combined with seymour duncan bassline pickups. the aguilar obp-3 is actually an excellent preamp, but it is voiced quite differently than the bartolini. it sounds a bit more transparent to me... doesn't have as much color in my opinion as the bartolini but depending on what you like to hear and what your pickup placement is, that can be a great thing or a not so great thing. the same pickup/preamp combinations will sound different in different basses.
